Cutting elements, methods for manufacturing such cutting elements, and tools incorporating such cutting elements

ABSTRACT

The present disclosure relates to cutting elements incorporating polycrystalline diamond bodies used for subterranean drilling applications, and more particularly, to polycrystalline diamond bodies having a high diamond content which are configured to provide improved properties of thermal stability and wear resistance, while maintaining a desired degree of impact resistance, when compared to prior polycrystalline diamond bodies. In various embodiments disclosed herein, a cutting element with high diamond content includes a modified PCD structure and/or a modified interface (between the PCD body and a substrate), to provide superior performance.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional application of U.S. patent applicationSer. No. 12/784,460 filed on May 20, 2010, which claims the benefit ofU.S. Provisional Patent Application Ser. No. 61/322,149 filed on Apr. 8,2010 and U.S. Provisional Patent Application Ser. No. 61/180,059 filedon May 20, 2009; all of which are incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

The present disclosure relates to cutting elements incorporatingpolycrystalline diamond bodies used for subterranean drillingapplications, and more particularly, to polycrystalline diamond bodieshaving a high diamond content which are configured to provide improvedproperties of thermal stability and wear resistance, while maintaining adesired degree of impact resistance, when compared to priorpolycrystalline diamond bodies.

BACKGROUND

Polycrystalline diamond (PCD) materials known in the art are formed fromdiamond grains (or crystals) and a catalyst material which are subjectedto high pressure and high temperature conditions (“HPHT sinteringprocess”). Such PCD materials are known for having a high degree of wearresistance, making them a popular material choice for use in suchindustrial applications as cutting tools for machining and wear andcutting elements in subterranean mining and drilling, where such highdegree of wear resistance is desired. In such applications, conventionalPCD materials can be provided in the form of a surface layer or body toimpart desired levels of wear resistance to a cutting tool.

Traditionally, PCD cutting elements include a substrate and a PCD bodyor layer attached thereto. Substrates used in such cutting elementapplications include carbides such as a cemented tungsten carbide (e.g.,WC—Co). Such conventional PCD bodies utilize a catalyst material tofacilitate intercrystalline bonding between the diamond grains and tobond the PCD body to the underlying substrate. Metals conventionallyemployed as the catalyst are often selected from the group of solventmetal catalysts including cobalt, iron, nickel, combinations and alloysthereof.

The amount of catalyst material used to form the PCD body represents acompromise between desired properties of strength/toughness/impactresistance and hardness/wear resistance/thermal stability. While ahigher metal catalyst content typically increases the strength,toughness and impact resistance of a resulting PCD body, such highermetal catalyst content also decreases the hardness and correspondingwear resistance as well as the thermal stability of the PCD body. Thus,these inversely affected properties ultimately limit the ability toprovide PCD bodies having desired levels of hardness, wear resistance,thermal stability, strength, impact resistance and toughness to meet theservice demands of particular applications, such as cutting and/or wearelements used in subterranean drilling devices.

A particularly desired property of PCD bodies used for certainapplications is improved thermal stability during wear or cuttingoperations. A problem known to exist with conventional PCD bodies isthat they are vulnerable to thermal degradation when exposed to elevatedtemperature cutting and/or wear applications. This vulnerability resultsfrom the differential that exists between the thermal expansioncharacteristics of the solvent metal catalyst material disposedinterstitially within the PCD body and the thermal expansioncharacteristics of the intercrystalline bonded diamond. Suchdifferential thermal expansion is known to start at temperatures as lowas 400° C., and can induce thermal stresses that can be detrimental tothe intercrystalline bonding of diamond and eventually result in theformation of cracks that can make the PCD structure vulnerable tofailure. Accordingly, such behavior is not desirable.

Another form of thermal degradation known to exist with conventional PCDmaterials is one that is also related to the presence of the solventmetal catalyst in the interstitial regions of the PCD body and theadherence of the solvent metal catalyst to the diamond crystals.Specifically, the solvent metal catalyst is known to cause an undesiredcatalyzed phase transformation in diamond (converting it to carbonmonoxide, carbon dioxide or graphite) with increasing temperature,thereby limiting practical use of the PCD body to about 750° C.

Thermal degradation can lead to chipping, spalling, partial fracturingand/or exfoliation of the PCD body. These problems can be caused by theformation of micro-cracks within the PCD body followed by propagation ofthe crack across the PCD body. Micro-cracks can form from thermalstresses occurring within the PCD body.

U.S. Pat. No. 6,601,662 (“the '662 patent”) relates to cutting elementscomprising a PCD body with improved wear resistance and methods ofmanufacturing such cutting elements. The cutting elements described havea PCD body having a diamond volume density of greater than 85% andcontain an interstitial matrix in the PCD body adjacent to a workingsurface which is substantially free of the catalyzing material. The '662patent teaches that in order to achieve a sufficient level of wearresistance, increasing the volume density of diamond leads to areduction in the depth of interstitial matrix which is substantiallyfree of catalyzing material.

U.S. Pat. No. 7,493,973 (“the '973 patent”) relates to cutting elementscomprising a PCD body with a high diamond content which is treated toprovide improved properties of abrasion resistance and thermalstability, while maintaining a desired degree of impact resistance. Thehigh diamond content is obtained using coarse-sized diamond grains, suchas diamond grains having an average particle size of about 0.03 mm orgreater. The '973 patent also teaches that the diamond volume content ofthe region of the PCD body to be treated (rendered substantially free ofcatalyst material) will impact the depth of treatment needed to obtain adesired level of performance such as wear resistance. In particular, the'973 patent teaches that for a diamond content of greater than about 93%by volume (% v), the average depth of treatment is less than about 0.08mm (millimeters) (80 microns/micrometers) and for a diamond content ofat least about 95% by volume (% v), the average depth of treatment is atmost about 0.03 mm (30 microns).

Although much work has been done with respect to the PCD body used toform a cutting element, it is still desirable that a PCD body bedeveloped that displays even greater improvements in properties such aswear resistance and thermal stability while not sacrificing desiredstrength, toughness or impact resistance, especially for difficultdrilling applications. Examples of difficult drilling applicationsinclude abrasive sandstones such as those found in the East Texas Basinand geothermal applications.

SUMMARY

The present disclosure relates to cutting elements incorporatingpolycrystalline diamond bodies used for subterranean drillingapplications, and more particularly, to polycrystalline diamond bodieshaving a high diamond content which are configured to provide improvedproperties of thermal stability and wear resistance, while maintaining adesired degree of impact resistance, when compared to priorpolycrystalline diamond bodies. In various embodiments disclosed herein,a cutting element with high diamond content includes a modified PCDstructure and/or a modified interface (between the PCD body and asubstrate), to provide superior performance.

In one embodiment, a cutting element includes a polycrystalline diamondbody comprising: an interface surface; a top surface opposite theinterface surface; a cutting edge meeting the top surface; and amaterial microstructure comprising a plurality of bonded-togetherdiamond crystals and interstitial regions between the diamond crystals.A first region of the microstructure proximate the cutting edgecomprises a plurality of the interstitial regions that are substantiallyfree of a catalyst material, and the first region extends from thecutting edge to a depth of at least 300 microns. A second region of themicrostructure proximate the interface surface comprises a plurality ofthe interstitial regions comprising the catalyst material disposedtherewithin. The first region comprises a sintered average grain sizeless than 25 microns. The first region has at least one of the followingproperties: an apparent porosity less than (0.1051)·(the average grainsize ̂-0.3737); or a leached weight loss less than (0.251)·(the averagegrain size ̂-0.2691); or a diamond volume fraction greater than(0.9077)·(the average grain size ̂ 0.0221), with the average grain sizeprovided in microns.

In one embodiment, a cutting element comprises a polycrystalline diamondbody comprising an interface surface; a top surface opposite theinterface surface; a cutting edge meeting the top surface; and amaterial microstructure comprising a plurality of bonded-togetherdiamond crystals and interstitial regions between the diamond crystals.A first layer of the microstructure proximate the cutting edge comprisesa first diamond volume fraction and a second layer of the microstructureproximate the interface surface comprises a second diamond volumefraction that is at least approximately 2% less than the first diamondvolume fraction. The first layer has at least one of the followingproperties: an apparent porosity less than (0.1051)·(the average grainsize ̂-0.3737); or a leached weight loss less than (0.251)·(the averagegrain size ̂-0.2691); or the first diamond volume fraction is greaterthan (0.9077)·(the average grain size ̂ 0.0221), with the average grainsize provided in microns.

In one embodiment, a cutting element includes a polycrystalline diamondbody comprising: an interface surface; a top surface opposite theinterface surface; a cutting edge meeting the top surface; and amaterial microstructure comprising a plurality of bonded-togetherdiamond crystals and interstitial regions between the diamond crystals.A first region of the microstructure proximate the cutting edgecomprises a plurality of the interstitial regions that are substantiallyfree of a catalyst material. The interface surface comprises aprotrusion ratio of less than 0.7. The first region comprises a sinteredaverage grain size less than 25 microns, and at least one of thefollowing properties: an apparent porosity less than (0.1051)·(theaverage grain size ̂-0.3737); or a leached weight loss less than(0.251)·(the average grain size ̂-0.2691); or a diamond volume fractiongreater than (0.9077)·(the average grain size ̂ 0.0221), with theaverage grain size provided in microns.

In one embodiment, a cutting element includes a substrate having aninterface surface, wherein the substrate comprises a cobalt content lessthan approximately 11% by weight; and a polycrystalline diamond bodyformed over the interface surface of the substrate. The polycrystallinediamond body comprises an interface surface; a top surface opposite theinterface surface; a cutting edge meeting the top surface; and amaterial microstructure comprising a plurality of bonded-togetherdiamond crystals and interstitial regions between the diamond crystals.A portion of the polycrystalline diamond body has at least one of thefollowing properties: an apparent porosity less than (0.1051)·(theaverage grain size ̂-0.3737), or a leached weight loss less than(0.251)·(the average grain size ̂-0.2691), or a diamond volume fractiongreater than (0.9077)·(the average grain size ̂ 0.0221), with theaverage grain size provided in microns.

In one embodiment, a cutting element comprises a polycrystalline diamondbody sintered at a sintering cold cell pressure greater than 5.4 GPa,the polycrystalline diamond body comprising: an interface surface; a topsurface opposite the interface surface; a cutting edge meeting the topsurface; and a material microstructure comprising a plurality ofbonded-together diamond crystals and interstitial regions between thediamond crystals. A first region of the microstructure proximate thecutting edge comprises a plurality of the interstitial regions that aresubstantially free of a catalyst material, and the first region extendsfrom the cutting edge to a depth of at least 300 microns. A secondregion of the microstructure proximate the interface surface comprises aplurality of the interstitial regions comprising the catalyst materialdisposed therewithin. The first region comprises a sintered averagegrain size less than 25 microns, and a diamond volume fraction greaterthan 92%.

In one embodiment, a cutting element comprises a polycrystalline diamondbody comprising: an interface surface; a top surface opposite theinterface surface; a cutting edge meeting the top surface; and amaterial microstructure comprising a plurality of bonded-togetherdiamond crystals and interstitial regions between the diamond crystals.A first region of the microstructure proximate the cutting edgecomprises a plurality of the interstitial regions that are substantiallyfree of a catalyst material, and the first region extends from thecutting edge to a depth of at least 300 microns. A second region of themicrostructure proximate the interface surface comprises a plurality ofthe interstitial regions comprising the catalyst material disposedtherewithin. The first region satisfies one of the following conditions:a sintered average grain size within the range of 2-4 microns, and adiamond volume fraction greater than 93%, or a sintered average grainsize within the range of 4-6 microns, and a diamond volume fractiongreater than 94%, or a sintered average grain size within the range of6-8 microns, and a diamond volume fraction greater than 95%, or asintered average grain size within the range of 8-10 microns, and adiamond volume fraction greater than 95.5%, or a sintered average grainsize within the range of 10-12 microns, and a diamond volume fractiongreater than 96%.

In one embodiment, a method of forming a polycrystalline diamond cuttingelement with high diamond content, comprises providing a catalystmaterial and a plurality of diamond particles; subjecting the catalystmaterial and the diamond particles to a high temperature and highpressure process, comprising applying a cold cell pressure within therange of approximately 5.4 GPa to 6.3 GPa and a temperature within therange of approximately 1400 to 1500° C., thereby forming apolycrystalline diamond body comprising a plurality of bonded-togetherdiamond crystals and interstitial regions between the diamond crystals,and comprising a cutting edge; and removing the catalyst material from afirst region of the diamond body proximate the cutting edge to render aplurality of the interstitial regions in the first region substantiallyempty, the first region extending to a depth of at least 300 micronsfrom the cutting edge.

In one embodiment, a method of forming a polycrystalline diamond cuttingelement with high diamond content, comprises providing a first diamondmixture; providing a second diamond mixture; subjecting the first andsecond diamond mixtures to a high temperature and high pressure processin the presence of a catalyst material, such high temperature and highpressure process comprising applying a cold cell pressure within therange of approximately 5.4 to 6.3 GPa and a temperature within the rangeof approximately 1400 to 1500° C., thereby forming a polycrystallinediamond body comprising a first layer formed from the first diamondmixture and a second layer formed from the second diamond mixture, eachlayer comprising a plurality of bonded-together diamond crystals andinterstitial regions between the diamond crystals. The first layer formsat least a portion of the cutting edge of the diamond body and has afirst diamond volume fraction, and the second layer forms at least aportion of an interface surface of the diamond body and has a seconddiamond volume fraction that is at least approximately 2% less than thefirst diamond volume fraction. The first layer comprises a sinteredaverage grain size less than 25 microns, and the first layer has atleast one of the following properties: an apparent porosity less than(0.1051)·(the average grain size ̂-0.3737), or a leached weight lossless than (0.251)·(the average grain size ̂-0.2691), or the firstdiamond volume fraction is greater than (0.9077)·(the average grain sizê 0.0221), with the average grain size provided in microns.

In one embodiment, a method of forming a polycrystalline diamond cuttingelement with high diamond content, comprises providing a plurality ofdiamond particles and a substrate material having a cobalt content ofless than approximately 11% by weight; subjecting the diamond particlesand the substrate material to a high temperature and high pressureprocess, comprising applying a cold cell pressure within the range ofapproximately 5.4 to 6.3 GPa and a temperature within the range ofapproximately 1400 to 1500° C., thereby forming a polycrystallinediamond body comprising a plurality of bonded-together diamond crystalsand interstitial regions between the diamond crystals. At least aportion of the polycrystalline diamond body comprises a sintered averagegrain size less than 25 microns, and the portion of polycrystallinediamond body has at least one of the following properties: an apparentporosity less than (0.1051)·(the average grain size ̂-0.3737), or aleached weight loss less than (0.251)·(the average grain size ̂-0.2691),or the first diamond volume fraction is greater than (0.9077)·(theaverage grain size ̂ 0.0221), with the average grain size provided inmicrons.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a drill bit incorporating a plurality ofcutting elements according to an embodiment of the present disclosure.

FIG. 2 is a perspective view of a cutting element including a PCD bodyand a substrate according to an embodiment of the present disclosure.

FIG. 3A is schematic representation of a region of a PCD body includinga catalyst material.

FIG. 3B is a schematic representation of a region of a PCD body that issubstantially free of a catalyst material, according to an embodiment ofthe present disclosure.

FIG. 4A is a vertical cross-sectional view of a cutting element with aPCD body including first and second regions, according to an embodimentof the present disclosure.

FIG. 4B is a vertical cross-sectional view of a cutting element with aPCD body including first and second regions, according to an embodimentof the present disclosure.

FIG. 5 a partial cross-sectional view of an interface including aprotrusion with a rounded top surface.

FIG. 6 is a partial cross-sectional view of an interface including aprotrusion with a flat top surface.

FIG. 7 is a vertical cross-sectional view of a cutting element with aPCD body including first, second, and third regions, according to anembodiment of the present disclosure.

FIG. 8 is a partial cross-sectional view of a drill bit incorporating aplurality of cutting elements, according to an embodiment of the presentdisclosure.

FIG. 9 is a vertical cross-sectional view of a substrate with a domedinterface surface, according to an embodiment of the present disclosure.

FIG. 10A is a diagram of apparent porosity versus average grain size forPCD samples sintered at three different pressures (10.2 ksi, 11.0 ksi,and 12.0 ksi).

FIG. 10B is a diagram of leaching weight loss versus average grain sizefor PCD samples sintered at three different pressures (10.2 ksi, 11.0ksi, and 12.0 ksi).

FIG. 10C is a diagram of diamond volume fraction (as measured by aDensity technique) versus average grain size for PCD samples sintered atthree different pressures (10.2 ksi, 11.0 ksi, and 12.0 ksi).

FIG. 11 is a diagram of pressure (in GPa) versus temperature (in ° C.),showing the formation of diamond at various pressures and temperatures.

FIG. 12 is a diagram of yield versus protrusion ratio for cuttingelements according to embodiments of the present disclosure with varyingsubstrate geometries.

FIG. 13 is a side view of a substrate with a stepped interface surface,according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

The present disclosure relates to cutting elements comprising apolycrystalline diamond (PCD) body having a high diamond content andimproved thermal characteristics. In various embodiments disclosedherein, a cutting element with high diamond content includes a modifiedPCD structure and/or a modified interface (between the PCD body and asubstrate), to provide superior performance.

The following disclosure is directed to various embodiments of theinvention. The embodiments disclosed have broad application, and thediscussion of any embodiment is meant only to be exemplary of thatembodiment, and not intended to intimate that the scope of thedisclosure, including the claims, is limited to that embodiment or tothe features of that embodiment.

Certain terms are used throughout the following description and claimsto refer to particular features or components. As one skilled in the artwould appreciate, different persons may refer to the same feature orcomponent by different names. This document does not intend todistinguish between components or features that differ in name only. Thedrawing figures are not necessarily to scale. Certain features andcomponents herein may be shown exaggerated in scale or in somewhatschematic form and some details of conventional elements may not beshown in the interest of clarity and conciseness.

In the following description and in the claims, the terms “including”and “comprising” are used in an open-ended fashion, and thus, should beinterpreted to mean “including, but not limited to . . . .”

As used herein, a plurality of items, structural elements, compositionalelements and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, quantities, amounts, and other numerical data may bepresented herein in a range format. It is to be understood that suchrange format is used merely for convenience and brevity and should beinterpreted flexibly to include not only the numerical values explicitlyrecited as the limits of the range, but also to include all theindividual numerical values or sub-ranges encompassed within that rangeas if each numerical value and sub-range is explicitly recited. Forexample, a numerical range of 1 to 4.5 should be interpreted to includenot only the explicitly recited limits of 1 to 4.5, but also includeindividual numerals such as 2, 3, 4 and sub-ranges such as 1 to 3, 2 to4, etc. The same principle applies to ranges reciting only one numericalvalue, such as “at most 4.5,” which should be interpreted to include allof the above-recited values and ranges. Further, such an interpretationshould apply regardless of the breadth of the range or thecharacteristic being described.

Any patent, publication, or other disclosure material, in whole or inpart, that is said to be incorporated by reference herein isincorporated herein only to the extent that the incorporated materialdoes not conflict with existing definitions, statements, or otherdisclosure material set forth in this disclosure. As such, and to theextent necessary, the disclosure as set forth herein supersedes anyconflicting material incorporated herein by reference. Any material, orportion thereof, that is said to be incorporated by reference herein,but which conflicts with existing definitions, statements, or otherdisclosure material set forth herein will only be incorporated to theextent that no conflict arises between that incorporated material andthe existing disclosure material.

When using the term “different” in reference to materials used, it is tobe understood that this includes materials that generally include thesame constituents, but may include different proportions of theconstituents and/or that may include differently sized constituents,wherein one or both operate to provide a different mechanical and/orthermal property in the material. The use of the terms “different” or“differ,” in general, are not meant to include typical variations inmanufacturing.

Referring to FIG. 1, a drill bit 10, specifically a fixed cutter drillbit, is shown. The drill bit 10 includes a bit body 12, which may beformed of a matrix material, such as a tungsten carbide powderinfiltrated with an alloy binder material, or may be a machined steelbody. The bit body 12 includes a threaded connection 14 at one end forcoupling the bit 10 to a drilling string assembly (not shown). The bitbody 12 also includes a bit face 29 having a cutting element supportstructure disposed thereon which, in this example, comprises a pluralityof blades 16 extending from the surface of the bit body. Each of theblades 16 includes a plurality of cutter pockets 26 formed therein alongthe periphery to accept and support a cutting element 20 positionedtherein. Drilling fluid flow courses 19 are disposed between adjacentblades.

The cutting elements 20 may include polycrystalline diamond compactcutting elements, which may also be referred to as “PCD cutters,” “shearcutters” or “cutters” 20. A perspective view of a cutting element 20 isshown, for example, in FIG. 2. Referring to FIG. 2, a PCD body 22 isbonded to a substrate material 24 to form the cutting element 20. ThePCD body 22 has an upper surface 22 a and a side surface 22 b. The uppersurface 22 a meets the side surface 22 b at a cutting edge 22 c. Thecutting edge is that portion of the cutting element which engages theformation during drilling. The cutting edge is illustrated in FIG. 2 asa sharp edge; however, in one or more alternative embodiments, thetransition between the upper surface 22 a and the side surface 22 b maycontain a beveled, curved or tapered surface.

The PCD body 22 bonded to the substrate 24 is sometimes referred to as adiamond body, diamond table or abrasive layer. The PCD body 22 containsa microstructure of randomly oriented diamond crystals bonded togetherto form a diamond matrix phase and a plurality of interstitial regionsinterposed between the diamond crystals. The lower surface 25 of the PCDbody 22 and the upper surface of the substrate 24 form the interface 28.The cutting element 20 has a central longitudinal axis 11. The cuttingelement illustrated in FIG. 2 is depicted as cylindrical; however, it isto be understood that any other shape may be suitable, such as ovoid,elliptical, etc., and these other shapes are contemplated as beingwithin the scope of the present disclosure. In one or more otherembodiments, the cutting element 20 may be used without a substrate 24.In one or more embodiments, the PCD body has an average thickness(between the lower surface 25 and the upper surface 22 a) of at least1.0 mm, suitably at least 1.5 mm, more suitably at least 2 mm, mostsuitably in the range of from 1.5 mm to 5 mm, for example 2.25 mm, 2.5mm, 2.75 mm, 3 mm, 3.25 mm, 3.5 mm, or 4 mm.

FIG. 3A schematically illustrates a region 310 of a PCD body thatincludes a catalyst material. In particular, the region 310 comprises aplurality of bonded together diamond crystals 312, forming anintercrystalline diamond matrix first phase, and catalyst material 314that is attached to the surfaces of the diamond crystals and/or disposedwithin the plurality of interstitial regions that exist between thebonded together diamond crystals (i.e., the interstitial regions are atleast partially filled with catalyst material). For purposes of clarity,it is understood that the region 310 of the PCD body may be one takenwithin the second region of the PCD body, as described below.

FIG. 3B schematically illustrates a region 322 of a PCD body that issubstantially free of the catalyst material. Like the PCD region 310illustrated in FIG. 3A, the region 322 includes a materialmicrostructure comprising a plurality of bonded together diamondcrystals 324, forming the intercrystalline diamond matrix first phase.Unlike the region 310 illustrated in FIG. 3A, this region 322 of the PCDbody has been treated to remove the catalyst material from the pluralityof interstitial regions and, thus, comprises a plurality of interstitialregions 326 that are substantially free of the catalyst material, i.e.,substantially empty voids (pores). At least a portion of the pores maybe interconnected. For the purposes of clarity, it is understood thatthe region 322 of the PCD body may be one taken within the first regionof the PCD body after a treatment process, as described below.

The term “filled”, as used herein to refer to the presence of thecatalyst material contained in the interstitial regions of the PCD body,is understood to mean that substantially all of the volume of theinterstitial regions (voids/pores) contain the catalyst material (andtungsten carbide, and/or trace amounts of other elements such asrefractory materials, including Nb, Ta, and Mo that may infiltrate intothe PCD; these materials typically react with carbon to form carbides).Also, tungsten carbide and/or trace amounts of Fe or Cr may be presentas a byproduct of diamond powder processing. However it is to beunderstood that there may also be a volume of interstitial regionswithin the same region of the PCD body that do not contain the catalystmaterial, and that the extent to which the catalyst material effectivelyfills the voids or pores will depend on such factors as the particularmicrostructure of the PCD body, the effectiveness of the process usedfor introducing the catalyst material, removal of absorbed gases fromthe surfaces of the diamond powders, and the desired mechanical and/orthermal properties of the resulting PCD body.

In one embodiment, a PCD body with high diamond content is provided. PCDwith high diamond content may be characterized as PCD with a highdiamond volume fraction (DVF). The diamond volume fraction refers to theratio by volume of diamond to the overall volume of the PCD region ofinterest (i.e., a portion of the PCD body (e.g., first or secondregions) or the entire PCD body). High diamond content can also becharacterized by the apparent porosity of the PCD sample, and theleaching weight loss, as described below.

In one embodiment, PCD with high diamond content is formed by HPHTsintering at higher than normal pressures, as shown for example in FIG.11. FIG. 11 shows a diagram of the pressures and temperatures used tocreate PCD (as is known in the art) and PCD with high diamond content(according to embodiments of the present disclosure). The diagramincludes two lines dividing the diagram into four quadrants. The morehorizontal line is the diamond/graphite equilibrium line, which is wellknown to those skilled in the art as the Berman-Simon line. Diamond isthermodynamically stable at pressures above this line. The more verticalline is the Co—C eutectic line, adopted from FIG. 16.7 of Field's wellknown reference book Properties of Diamond, Academic Press, 1979. Attemperatures to the right of this line, cobalt is liquid in form, and attemperatures to the left, it is in solid form. In industrial practice,diamond is formed in the top right quadrant, above the diamond/graphiteline and to the right of the cobalt line.

As indicated in FIG. 11, standard HPHT pressures used to create PCD areinternal cold (room temperature) cell pressures in the range ofapproximately 4.6 to 5.4 GPa (gigapascals) (measured by the manganinresistance method, calibrated with bismuth and ytterbium transitions, atechnique well known in the industry). This pressure range becomesapproximately 5.5 to 6.2 GPa as temperatures are increased beyond thecobalt line, due to thermal expansion of the cell materials. The effectof temperature on cell pressure can be assessed using techniques knownin the industry, such as the melting point of gold. The lower pressurelimit is determined by the diamond/graphite line of the phase diagram.

In accordance with embodiments of the present disclosure, the higherpressures used to create PCD with high diamond content are approximately5.4 GPa to 6.3 GPa (cold cell pressures), which correspond toapproximately 6.2 GPa to 7.1 GPa as temperatures are increased past thecobalt/carbon eutectic line. In exemplary embodiments, the pressure (athigh temperature) is in the range of approximately 6.2 to 7.2 GPa. Invarious embodiments, the cell pressure (at high temperature) may begreater than 6.2 GPa, for example in the range of from greater than 6.2GPa to 8 GPa or from 6.3 GPa to 7.4 GPa, such as 6.25 GPa, 6.35 GPa, 6.4GPa, 6.45 GPa, 6.5 GPa, 6.6 GPa, or 6.7 GPa.

The temperatures used in both standard HPHT sintering and the higherpressure HPHT sintering used to create high diamond content are similar,ranging from approximately 1400° C. to 1450° C. Temperatures may beslightly higher for high diamond content HPHT sintering than forstandard HPHT sintering. Suitably, the temperatures used during the highpressure HPHT sintering process may be in the range of from 1350° C. to1500° C., for example 1400° C. to 1500° C., or for example from 1400° C.to 1450° C. Temperatures typically are kept around 1450° C. or below,and are not raised much beyond 1500° C., due to the resulting reactionsin the surrounding cell materials (niobium/tantalum reactions andsalt-NaCl melt).

After the HPHT sintering process is completed, the assembly may beremoved from the HPHT device (e.g., a cubic press, a belt press, atorroid press, etc.) and the cutting element removed from the assembly.The PCD body may be formed without using a substrate if desired.

The mixture of diamond grains (natural or synthetic) and catalystmaterial may be subjected to sufficient HPHT conditions for apre-determined period of time to sinter the diamond crystals forming thepolycrystalline diamond body, as described herein, and optionally, tobond the polycrystalline diamond body to a substrate. Suitable internalcold cell pressures required to obtain a given diamond content, catalystcontent, and density depend on several factors such as the amount andtype of catalyst present as well as the particle size and distributionof the diamond crystals used to form the PCD body, and the addition ofgraphite (whether by directly adding graphite to the diamond mixture orby graphitizing the diamond crystals in the diamond mixture, asdescribed in U.S. Patent Application No. 2008/0302579, filed Jun. 5,2007, which description is herein incorporated by reference). In thevarious examples described below, no graphite was added to the powdermixtures. The diamond powders were subjected to a 1280° C. vacuumenvironment for 1-2 hours before sintering. No graphite was detectableby subsequent examination of the powder by Raman spectroscopy, which iswell known in the art as a standard carbon phase characterizationtechnique.

In one embodiment, a PCD body with high diamond content includes adiamond volume fraction (v_(dia) or DVF) of greater than 90%, and inanother embodiment greater than 91%, and in other embodiments greaterthan 92%, 92.5%, 93%, 94%, 95%, 95.5%, 96%, 97%, 98%, or 99%.

Three different techniques are provided herein for identifying PCD withhigh diamond content. First, the apparent porosity of thehigh-diamond-content PCD body can be determined. Second, the leachingweight loss of the PCD body can be determined. Third, the DVF of thesample can be determined. Each of these three properties, in connectionwith the grain size of the sintered PCD sample, can be used to identifya PCD sample as having high diamond content. Techniques for determiningthese three properties of a PCD sample are presented below.Additionally, PCD bodies were tested with each method to evaluate themethods and correlate results. As explained below, PCD bodies with highdiamond content made in accordance with embodiments of the presentdisclosure can be identified by one (or more) of these three methods,based on the procedures, assumptions, and limitations described below.The methods are referred to as the (1) Apparent Porosity, (2) WeightLoss and (3) Density methods. The apparent porosity and weight lossmethods can be used to identify PCD bodies created at higher than normalpressures, without assuming or determining an amount of cobalt in thePCD body, while the density method requires determination of the cobaltto tungsten ratio in the sintered body.

The first method for assessing the diamond content of a sintered PCDbody or a region or portion of the PCD body (referred to as the PCDsample) is the “Apparent Porosity” method. The apparent porosity of asample is the percentage by volume of voids over the total volume of thesample. The apparent porosity method measures the volume of voids in thesample. PCD with high diamond content has fewer voids, as more of thevolume of the sample is occupied by diamond crystals.

This method includes leaching a sintered PCD sample to remove the metalcatalyst in the interstitial regions between the diamond crystals,measuring the weight of the leached sample, and then immersing it inwater and weighing again to determine the increased weight from thepermeation of water into the leached interstitial regions. Based on theincrease in weight from the water, the volume of the interstitialregions can be determined.

An embodiment of this method is described in more detail as follows.First, the PCD sample is leached according to the following procedure.Complete leaching is achieved in the PCD sample by placing the sample inan acid solution in a Teflon container, which is contained within asealed stainless steel pressure vessel and heated to 160-180° C.Containers suitable for such leaching procedures are commerciallyavailable from Bergoff Products & Instruments GmbH, Eningen, Germany. Itis likely that pressures of between 100-200 psi are achieved by heatingunder these conditions, though during the inventors' actual testing(summarized below), the pressure was not directly measured. A standardacid solution which has been found to work satisfactorily in leachingPCD material is made from reagent grade acids and comprises aconcentration of approximately 5.3 mol/liter HNO₃ and approximately 9.6mol/liter HF, which is made by ratio of 1:1:1 by volume of HNO₃—15.9mol/liter (reagent grade nitric acid): HF—28.9 mol/liter (reagent gradehydrofluoric acid): and water.

Second, verification of the leaching process is performed by examiningthe leached PCD sample with penetrating x-ray radiography to confirmthat the acid mixture penetrated the sample and that no macro-scalecatalytic metallic regions remain. During the inventors' testing, it wasfound that typically a time period between 2-3 weeks in the pressurevessel was adequate to sufficiently leach the catalytic metals from thePCD sample.

Third, subsequent to leaching and verification, the sample is cleaned ofresidual materials such as nitrates and insoluble oxides by alternatingexposure to deionized water in the pressure vessel described above(dilution of the soluble nitrates) and exposing the sample to ultrasonicenergy at room temperature (removal of insoluble oxides). Repeating thecycle of high temperature/pressure deionized water/ultrasonic energyexposure three times was found to be sufficient to adequately clean thesample.

The above procedure completes the leaching and preparation of thesample. Next, the apparent porosity method is performed according to theASTM (American Society for Testing and Materials) C20 standard fordetermining apparent porosity of a sample. Specifically, after leachingand cleanup, the prepared sample is weighed to determine the leachedweight (W_(L)). Next, the sample is submerged in boiling water for atleast two hours to infiltrate water into the leached interstitialregions (pores) of the PCD sample. After cooling, the infiltrated,submerged sample is weighed in water to determine the leached,infiltrated, submerged weight (W_(LIS)). The sample is then gripped witha paper towel and removed from the water. Water remains trapped in theinternal pores of the sample. The sample is then weighed to determinethe leached and infiltrated weight in air (W_(LI)).

With these values, the apparent porosity (AP) of the sample can bedetermined with the following equation:

$\begin{matrix}{{AP} = \frac{\left( {W_{LI} - W_{L}} \right)}{\left( {W_{LI} - W_{LIS}} \right)}} & (1)\end{matrix}$

That is, the apparent porosity AP is the increase in weight of theleached sample after boiling water infiltration (W_(LI)−W_(L)) dividedby the difference in weight of the leached and infiltrated sample afterbeing submerged. This value shows the percentage by volume of emptypores in the leached sample.

As mentioned above, a PCD sample with high diamond content tends to havelow apparent porosity, as a high percentage of the volume of the sampleis occupied by the diamond crystals, rather than the pores between thecrystals. Notably, the above method operates on the assumption that thePCD sample is fully leached, meaning that all metal content is removedfrom the PCD sample, leaving only diamond behind. The apparent porositymeasures interconnected porosity—the increase in weight due to waterinfiltration into the interconnected leached pores. However, some poresare isolated and not reached by the water, or are too small orinterconnected by channels that are too fine to permit entry of thewater. Other pores may remain partially occupied by metal and thus willnot be fully infiltrated by the water. These various un-infiltratedpores are not included in the above calculation of apparent porosity.The above method can be used to calculate the interconnected porosity ofvarious PCD samples, and compare the porosity to identify samples withhigh diamond content.

Four different diamond powders were HPHT sintered at three differenthigh pressures to form twelve PCD bodies with high diamond content fortesting according to the above method. The parameters of the fourdiamond powder mixtures are shown below in Table I:

TABLE I Starting Sintering Grain Aids Size Constituent Diamond Cuts (wt%) (wt %) Mixture (micron) 25~45 25~40 20~30 16~26 12~22 8~16 6~12 4~83~6 2~4 1~3 Co 1 25 14% 24% 12% 15% 24%  6%  5% 2 2 16 28% 44% 7% 16% 5% 2 3 12 50% 38% 12% 2 4 5 88% 12% 2

The four powder mixtures listed above were sintered at three differenthigh pressures (hydraulic fluid pressures of 10.2 ksi, 11 ksi, and 12ksi) (which correlate to internal cold cell pressures of 5.4 GPa, 5.8GPa, and 6.2 GPa, and internal hot cell pressures of 6.2 GPa, 6.7 GPa,and 7.1 GPa). These sintered PCD bodies were then tested according tothe method presented above to identify the apparent porosity of thesintered PCD bodies. The results are shown in FIG. 10A. FIG. 10A showsthe measured apparent porosity versus sintered average sintered grainsize, for three different sintering pressures.

The average grain size of a PCD sample can be determined by an electronback scatter diffraction (EBSD) technique, as follows. A suitablesurface preparation is achieved by mounting and surfacing the PCD sampleusing standard metallographic procedures, and then subsequentlyproducing a mirror surface by contact with a commercially available highspeed polishing apparatus (available through Coborn Engineering CompanyLimited, Romford, Essex, UK). The EBSD data is collected in a scanningelectron microscope suitably equipped to determine grain orientation bylocalized diffraction of a directed electron beam (available throughEDAX TSL, Draper, Utah, USA). Magnification is selected such thatgreater than 1000 grains were included in a single image analysis, whichwas typically between 500×-1000× for the grain sizes examined. Duringthe inventors' testing, other conditions were as follows: voltage=20 kV,spot size=5, working distance=10-15 mm, tilt=70°, scan step=0.5-0.8microns. Grain size analysis is performed by analysis of the collecteddata with a misorientation tolerance angle=2°. Defined grain areasdetermined according to the above conditions are sized according to theequivalent diameter method, which is mathematically defined asGS=(4A/π)^(1/2), where GS is the grain size and A is the grain area.This analysis provided the average grain size for each of the sinteredPCD samples.

The powder mixtures identified above were sintered at three differentpressures, and the PCD samples were tested according to the abovemethods to identify the apparent porosity and sintered average grainsize. The resulting measurements are shown in Table II as follows:

TABLE II Apparent Porosity Weight Weight Leached- Weight Leached-Sintered Average Pressure Leached Infiltrated Infiltrated-SubmergedApparent Grain Size Mixture (ksi) (gm) (gm) (gm) Porosity (micron) 110.2 0.9618 0.9727 0.6898 0.0387 13.5 2 10.2 0.9899 1.0029 0.7106 0.04459.8 3 10.2 0.9831 0.9978 0.7059 0.0503 8.2 4 10.2 0.7133 0.7282 0.51360.0696 2.9 1 11 0.9508 0.9609 0.6826 0.0363 13.5 2 11 0.9775 0.98910.7017 0.0404 9.8 3 11 0.9542 0.9672 0.6854 0.0460 8.2 4 11 0.95970.9775 0.6913 0.0622 2.9 1 12 1.0096 1.0198 0.7251 0.0348 13.5 2 121.0103 1.0215 0.7259 0.0381 9.8 3 12 0.9893 1.0008 0.7112 0.0399 8.2 412 0.9585 0.9739 0.6911 0.0546 2.9

This data is plotted in FIG. 10A. As shown in FIG. 10A, the relationshipbetween apparent porosity and sintered average grain size followed thesame trend for the three different sintering pressures. Curve fits wereapplied to the data, and the resulting equations are shown on the chartfor each sintering pressure. For a given grain size, increasing thesintering pressure led to a decrease in apparent porosity. This is dueto the higher pressure causing additional compaction of the diamondpowder, resulting in smaller voids between the sintered diamondcrystals.

FIG. 10A also shows that for a given sintering pressure, increasing theaverage grain size leads to a decrease in apparent porosity. This resultis likely due the fracturing of the larger diamond crystals during theHPHT sintering. Finer diamond crystals are more resistant to fracturingthan the larger diamond crystals, which fracture and rearrangethemselves under pressure, compacting and packing more effectively intothe spaces between the crystals, as discussed again in more detailbelow.

The curve fit for the 10.2 ksi data in FIG. 10A identifies the boundarybetween high and standard sintering pressures. Thus, a PCD sample can beidentified as having been sintered at high sintering pressure bymeasuring the sintered average grain size and the apparent porosity ofthe sample. For a given grain size, if the apparent porosity is belowthe 10.2 ksi line, then the sample was sintered at higher than standardsintering pressures. If the apparent porosity is above the 10.2 ksiline, then the sample was sintered at standard pressures. As mentionedabove, the hydraulic fluid pressure of 10.2 ksi corresponds to aninternal cold cell pressure of 5.4 GPa and a hot cell pressure of 6.2GPa.

Accordingly, PCD with high diamond content, formed by sintering athigher than normal pressures, can be identified as follows (with averagegrain size in microns):

PCD with an apparent porosity less than (0.1051)·(the average grain sizê-0.3737), or

PCD with an apparent porosity less than (0.091)·(the average grain sizê-0.3471), or

PCD with an apparent porosity less than (0.0744)·(the average grain sizê-0.2932), or

PCD with an apparent porosity less than one of the following values andan average grain size within the corresponding range:

Sintered Apparent Apparent Apparent Average Grain Porosity PorosityPorosity Size (micron) (12 ksi) (11 ksi) (10.2 ksi) 2-4 0.050 0.0560.063 4-6 0.044 0.049 0.054 6-8 0.040 0.044 0.048  8-10 0.038 0.0410.044 10-12 0.036 0.038 0.042

The second method for assessing the diamond content of a PCD body isreferred to as the “Weight Loss” method. This method includes measuringthe weight of the sample before and after leaching to determine theamount of metal removed. The ratio of the weight of metal removed byleaching to the total weight of the sample is referred to as the“leaching weight loss(%).” Optionally, additional measurements can betaken (including the mass fractions of the metal components) in order toconvert the weight loss into a volume fraction and determine the metalvolume fraction, as shown below.

An embodiment of this method is described in more detail as follows.Before leaching the PCD sample, the sample is weighed in air to obtainthe unleached weight (W_(U)), and weighed in water to obtain theunleached, submerged weight (W_(US)). Next, the PCD sample is leached,leaching is verified and the sample is cleaned according to the samesteps outlined above for the Apparent Porosity method. These stepscomplete the leaching and preparation of the sample.

Next, the leached, cleaned sample is weighed to obtain the leachedweight (W_(L)). The leaching weight loss is then calculated as follows:

$\begin{matrix}{{{Leaching}\mspace{14mu} {Weight}\mspace{14mu} {Loss}\mspace{14mu} (\%)} = \frac{\left( {W_{U} - W_{L}} \right)}{W_{U}}} & (2)\end{matrix}$

Optionally, the following calculations can be used to determine themetal volume fraction of the PCD sample, which can be used to estimatethe diamond volume fraction as well:

$\begin{matrix}{{{Metal}\mspace{14mu} {Volume}\mspace{14mu} {Fraction}\mspace{14mu} ({MVF})} = \frac{\rho_{S}\left( {W_{U} - W_{L}} \right)}{\rho_{M}\left( W_{U} \right)}} & (3) \\{{{{where}\mspace{14mu} \rho_{S}} = {{{density}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} {sample}} = \frac{\rho_{W}W_{U}}{W_{U} - W_{US}}}}{{{and}\mspace{14mu} \rho_{W}} = {{{density}\mspace{14mu} {of}\mspace{14mu} {water}} = {1.00\mspace{14mu} {gm}\text{/}{cc}}}}} & (4) \\{{{{and}\mspace{14mu} \rho_{M}} = {{{density}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} {metal}} = \frac{\rho_{WC}{\rho_{CO}\left( {m_{CO} + m_{WC}} \right)}}{{m_{CO}\rho_{WC}} + {m_{WC}\rho_{CO}}}}}{{{and}\mspace{14mu} m_{CO}} = {{mass}\mspace{14mu} {fraction}\mspace{14mu} {of}\mspace{14mu} {cobalt}}}{{{and}\mspace{14mu} m_{WC}} = {{mass}\mspace{14mu} {fraction}\mspace{14mu} {of}\mspace{14mu} {tungsten}\mspace{14mu} {carbide}}}} & (5)\end{matrix}$

The densities of cobalt (ρ_(CO)) and tungsten carbide (ρ_(WC)) areknown. Thus, to complete the equations above, the mass fractions ofcobalt (m_(CO)) and tungsten (m_(WC)) must be determined. These massfractions can be determined by analytical techniques such as energydispersive spectroscopy (EDS), which is described in further detailbelow in connection with the third “Density” method.

With the above equations, diamond volume fraction may be estimated fromeither the Apparent Porosity or the Weight Loss methods. However itshould be recognized that calculation of DVF by those techniques hasinherent differences from the Density method (described below), and isnot considered to be equivalent to the Density method. Calculation ofDVF by the Weight Loss method relies on analytical techniques todetermine the mass fractions of the metal components in the sintered PCDsample. It also relies on leaching to fully remove the metal from thePCD, so that the difference in weight can be obtained. Accordingly, thismethod is likely to slightly under-estimate the total metal content, assome metal content may remain in trapped pores within the PCD sampleeven after leaching. The same limitation applies to calculation of DVFby the Apparent Porosity method, which relies on leaching and waterinfiltration. Herein, references to DVF are DVF measured according tothe Density method.

Accordingly, the Weight Loss method uses the leached and unleachedweights of the PCD sample to determine the leaching weight loss %. Thesame PCD samples identified above in the Apparent Porosity method (thefour diamond powder mixtures sintered at three different pressures) weretested according to the Weight Loss method to determine and compare theleaching weight loss of the samples. The resulting measurements areshown in Table III:

TABLE III Weight Loss Sintered Weight Weight Weight Leaching AveragePressure Unleached Leached Loss Weight Co wt % W wt % Grain Size Mixture(ksi) (gm) (gm) (gm) Loss (%) (EDS) (EDS) (micron) 1 10.2 1.0950 0.96170.1333 12.17% 10.51 2.32 13.5 2 10.2 1.1222 0.9718 0.1504 13.40% 11.413.12 9.8 3 10.2 1.1576 0.9843 0.1733 14.97% 12.15 3.62 8.2 4 10.2 0.88850.7233 0.1652 18.59% 15.01 5.29 2.9 1 11 1.0853 0.9603 0.1249 11.51%11.43 3.2 13.5 2 11 1.1217 0.9821 0.1396 12.45% 11.54 3.01 9.8 3 111.1087 0.9541 0.1546 13.94% 12.01 3.36 8.2 4 11 1.1603 0.9587 0.201617.37% 14.83 6.28 2.9 1 12 1.1263 1.0055 0.1208 10.73% 10.53 2.89 13.5 212 1.1414 1.0102 0.1311 11.49% 14.42 5.740 9.8 3 12 1.1372 0.9926 0.144612.71% 11.97 4.02 8.2 4 12 1.1307 0.9535 0.1772 15.67% 16.33 5.24 2.9

This data is also plotted in FIG. 10B, which shows the leaching weightloss (%) versus the measured sintered average grain size. As shown inFIG. 10B, the relationship between leaching weight loss and averagegrain size followed the same trend for the three different sinteringpressures. Curve fits were applied to the data, and the resultingequations are shown on the chart for each sintering pressure. For agiven grain size, increasing the sintering pressure led to a decrease inthe leaching weight loss. This is due to the higher pressure causingadditional compaction of the diamond grains, resulting in smaller voidsbetween the sintered diamond crystals, and less metal infiltrating thevoids during sintering. The lower metal content leads to a lowerleaching weight loss.

FIG. 10B also shows that for a given sintering pressure, increasing theaverage grain size leads to a decrease in leaching weight loss. Thisresult is likely due the fracturing of the larger diamond crystalsduring the HPHT sintering, as discussed above. The finer diamondcrystals fracture and rearrange themselves under pressure, compactingand packing more effectively into the spaces between the crystals,leading to lower metal content infiltrating the PCD body duringsintering.

The curve fit for the 10.2 ksi data in FIG. 10B identifies the boundarybetween high and standard sintering pressures. Thus, a PCD sample can beidentified as having been sintered at high sintering pressure bymeasuring the average grain size and the leaching weight loss of thesample. For a given grain size, if the leaching weight loss is below the10.2 ksi line, then the sample was sintered at higher than standardsintering pressures. If the leaching weight loss is above the 10.2 ksiline, then the sample was sintered at standard pressures.

Accordingly, PCD with high diamond content, formed by sintering athigher than normal pressures, can be identified as follows (with averagegrain size in microns):

PCD with a leaching weight loss less than (0.251)·(the average grainsize ̂-0.2691), or

PCD with a leaching weight loss less than (0.2328)·(the average grainsize ̂-0.2653), or

PCD with a leaching weight loss less than (0.2052)·(the average grainsize ̂-0.2455), or

PCD with a leaching weight loss less than one of the following valuesand an average grain size within the corresponding range:

Sintered Leaching Leaching Leaching Average Grain Weight Loss WeightLoss Weight Loss Size (micron) (12 ksi) (11 ksi) (10.2 ksi) 2-4 0.1460.161 0.174 4-6 0.132 0.145 0.156 6-8 0.123 0.134 0.144  8-10 0.1170.126 0.136 10-12 0.111 0.120 0.129

The third method for assessing the diamond content of a PCD sample isreferred to as the “Density” method. This method calculates the diamondvolume fraction of the PCD sample. This method does not require leachingof the PCD sample. Instead, the bulk density of the sample is measured,and the ratios of metal components and diamond are measured to determinethe volume fractions of these components.

This method includes determining the component mass fractions byanalytical methods. Determination of the binder composition can employone of many techniques, including energy dispersive spectroscopy (EDS),wavelength dispersive spectroscopy (WDS), x-ray fluorescence (XRF),inductively coupled plasma (ICP), or wet chemistry techniques. Becauseof its frequent usage in scanning electron microscopes, EDS is commonlyused to quantitatively assess PCD specimens. However, EDS may notaccurately determine low atomic number elements such as carbonaccurately without arduous effort, which causes problems in a materialsuch as PCD. Despite this known limitation, if the cobalt/tungsten ratioof the binder phase is known with reasonable accuracy, then thecomposition can be reasonably determined if the bulk density of thesample is known.

To determine if any individual analytical method such as those mentionedabove is sufficiently calibrated, analysis of a known cemented carbidesample should be performed. Sufficient accuracy is obtained if thecobalt elemental composition is within 0.5% and the tungsten elementalcomposition is within 1.5% (i.e. a WC-13 wt % Co should give 12.5-13.5wt % cobalt and 80.1-83.1 wt % tungsten). More reliable EDS results onPCD samples are obtained when the sample is polished to mirror surfacefinish by polishing with a diamond-containing grinding surface (e.g., agrinding wheel) similar to the method subsequently described for EBSDsample preparation. A low magnification 10-100× is typically used inorder to maximize the sampling region. Various working distances andaccelerating voltages can be employed, however, working distances of10-11 mm and accelerating voltage of 20 kilovolts have given acceptableresults. When analyzing a sample, the total time should include a livecollection time of 30-60 seconds with a dead time of 25-35%. The EDSmeasured mass fractions may be used to determine a value for a constantk (see Equation 6 below). This constant k along with the measureddensity of the PCD body (ρ_(S) above) may be used to obtain thecalculated mass fractions of the diamond, catalyst and metal carbide(see Equations 7-9 below). The calculated volume fraction of diamond,catalyst and metal carbide may then be determined from the calculatedmass fractions (see Equations 10-12 below).

k=m _(catalyst) /m _(metal carbide)  (Equation 6)

-   -   where:        -   m_(catalyst) is the mass fraction determined from EDX            spectroscopy        -   m_(metal carbide) is the mass fraction of the metal            component in the metal carbide determined from EDX            spectroscopy

For example, if the catalyst material is cobalt and the metal carbide istungsten carbide, the following equations may be used to calculate themass fractions of the diamond (m_(dia)), cobalt (m_(co)), and tungstencarbide (m_(wc)) in the PCD body:

$\begin{matrix}{m_{dia} = {1 - {\frac{\left( {\rho_{dia} - \rho} \right)}{\rho}\left\lbrack \frac{\rho_{co}{\rho_{wc}\left( {k + 1} \right)}}{{\rho_{dia}\rho_{co}} + {\rho_{wc}\rho_{dia}k} - {\rho_{wc}{\rho_{co}\left( {k + 1} \right)}}} \right\rbrack}}} & \left( {{Equation}\mspace{14mu} 7} \right) \\{m_{co} = {\frac{\left( {\rho_{dia} - \rho} \right)}{\rho}\left\lbrack \frac{\rho_{co}\rho_{wc}k}{{\rho_{dia}\rho_{co}} + {\rho_{wc}\rho_{dia}k} - {\rho_{wc}{\rho_{co}\left( {k + 1} \right)}}} \right\rbrack}} & \left( {{Equation}\mspace{14mu} 8} \right) \\{m_{wc} = {\frac{\left( {\rho_{dia} - \rho} \right)}{\rho}\left\lbrack \frac{\rho_{co}\rho_{wc}}{{\rho_{dia}\rho_{co}} + {\rho_{wc}\rho_{dia}k} - {\rho_{wc}{\rho_{co}\left( {k + 1} \right)}}} \right\rbrack}} & \left( {{Equation}\mspace{14mu} 9} \right)\end{matrix}$

where:

-   -   ρ_(dia)=3.51 gm/cc    -   ρ_(co)=8.85 gm/cc    -   ρ_(wc)=15.7 gm/cc    -   ρ=measured density of the PCD sample

From the calculated mass fractions, the volume fractions may becalculated for diamond (v_(dia)), cobalt (v_(co)) and tungsten carbide(v_(wc)) in the PCD body using the following equations:

$\begin{matrix}{v_{dia} = \left\lbrack \frac{m_{dia}/\rho_{dia}}{{m_{dia}/\rho_{dia}} + {m_{co}/\rho_{co}} + {m_{wc}/\rho_{wc}}} \right\rbrack} & \left( {{Equation}\mspace{14mu} 10} \right) \\{v_{co} = \left\lbrack \frac{m_{{co}/}\rho_{co}}{{m_{dia}/\rho_{dia}} + {m_{co}/\rho_{co}} + {m_{wc}/\rho_{wc}}} \right\rbrack} & \left( {{Equation}\mspace{14mu} 11} \right) \\{v_{wc} = \left\lbrack \frac{m_{{wc}/}\rho_{wc}}{{m_{dia}/\rho_{dia}} + {m_{co}/\rho_{co}} + {m_{wc}/\rho_{wc}}} \right\rbrack} & \left( {{Equation}\mspace{14mu} 12} \right)\end{matrix}$

One skilled in the art would appreciate that the mass fractions andvolume fractions may be determined in a similar way when using acatalyst material other than cobalt and a metal carbide other thantungsten carbide, and the above equations may be modified as appropriateif significant amounts of additional materials are present.

The same PCD samples identified above in the Apparent Porosity andWeight Loss methods (the four diamond powder mixtures sintered at threedifferent pressures) were tested according to the Density method todetermine and compare the diamond volume fraction of the samples. Theresulting measurements are shown in Table IV:

TABLE IV Density Sample Sintered Average Pressure Co wt % W wt % Co/WDensity Diamond Vol Grain Size Mixture (ksi) (EDS) (EDS) Ratio (gm/cc)Fraction (micron) 1 10.2 10.51 2.32 4.53 3.874 0.9615 13.5 2 10.2 11.413.12 3.66 3.902 0.9559 9.8 3 10.2 12.15 3.62 3.36 3.955 0.9499 8.2 410.2 15.01 5.29 2.84 4.076 0.9295 2.9 1 11 11.43 3.2 3.57 3.844 0.963913.5 2 11 11.54 3.01 3.83 3.881 0.9587 9.8 3 11 12.01 3.36 3.57 3.9300.9532 8.2 4 11 14.83 6.28 2.36 4.046 0.9371 2.9 1 12 10.53 2.89 3.643.827 0.9653 13.5 2 12 14.42 5.740 2.51 3.857 0.9619 9.8 3 12 11.97 4.022.98 3.907 0.9580 8.2 4 12 16.33 5.24 3.12 4.009 0.9439 2.9

This data is also plotted in FIG. 10C, which shows the diamond volumefraction versus the measured average grain size. As shown in FIG. 10C,the relationship between diamond volume fraction and average grain sizefollowed the same trend for the three different sintering pressures.Curve fits were applied to the data, and the resulting equations areshown on the chart for each sintering pressure. FIG. 10C shows that thediamond volume fraction depends on the average grain size of the PCDsample. The DVF increases with average grain size (as shown by theupward slope). For a given sintering pressure, increasing the averagegrain size leads to an increase in diamond volume fraction. This resultis likely due to fracturing of the coarser diamond grains, as discussedabove.

Additionally, for a given grain size, increasing the sintering pressureled to an increase in the diamond volume fraction. This is due to thehigher pressure causing additional compaction of the diamond grains,resulting in smaller voids between the sintered diamond crystals, and ahigher density of diamond.

The curve fit for the 10.2 ksi data in FIG. 10C identifies the boundarybetween high and standard sintering pressures. Thus, a PCD sample can beidentified as having been sintered at high sintering pressure bymeasuring the average grain size and the diamond volume fraction of thesample. For a given grain size, if the diamond volume fraction is abovethe 10.2 ksi line, then the sample was sintered at higher than standardsintering pressures. If the diamond volume fraction is below the 10.2ksi line, then the sample was sintered at standard pressures.

Accordingly, PCD with high diamond content, formed by sintering athigher than normal pressures, can be identified as follows (with averagegrain size in microns):

PCD with a diamond volume fraction greater than (0.9077)·(the averagegrain size ̂ 0.0221), or

PCD with a diamond volume fraction greater than (0.9187)·(the averagegrain size ̂ 0.0183), or

PCD with a diamond volume fraction greater than (0.9291)·(the averagegrain size ̂ 0.0148), or

PCD with a diamond volume fraction greater than one of the followingvalues and an average grain size within the corresponding range:

Sintered Diamond Volume Diamond Volume Diamond Volume Average GrainFraction Fraction Fraction Size (micron) (12 ksi) (11 ksi) (10.2 ksi)2-4 0.939 0.930 0.922 4-6 0.948 0.942 0.936 6-8 0.954 0.949 0.944  8-100.958 0.954 0.950 10-12 0.961 0.958 0.955

Based on the relationships shown in FIG. 10C, in one embodiment, a PCDsample with high diamond content includes a sintered average grain sizewithin the range of 2-4 microns, and a diamond volume fraction greaterthan 93%; or a sintered average grain size within the range of 4-6microns, and a diamond volume fraction greater than 94%; or a sinteredaverage grain size within the range of 6-8 microns, and a diamond volumefraction greater than 95%; or a sintered average grain size within therange of 8-10 microns, and a diamond volume fraction greater than 95.5%;or a sintered average grain size within the range of 10-12 microns, anda diamond volume fraction greater than 96%.

For a given diamond grain size, a higher HPHT pressure creates a cuttingelement with a lower density. Lower density at higher pressure resultsbecause the diamond grains have a lower density than the catalystmaterial that infiltrates into the diamond layer during sintering.Higher pressure leads to a higher percentage of diamond than catalystmaterial, as the higher pressure forces the diamond crystals closertogether. This reduces the open space between the diamond crystals wherethe catalyst material can infiltrate the diamond layer. As a result,density of the PCD body is decreased.

As shown in FIG. 10C, the coarser diamond powder mixtures with largernominal grain size resulted in PCD bodies with a lower metal content.This is likely due to the fracturing of the larger diamond crystalsduring the HPHT sintering. Finer diamond crystals are more resistant tofracturing than the larger diamond crystals, which fracture andrearrange themselves under pressure, compacting and packing moreeffectively into the spaces between the crystals and leaving less spacefor metal from the substrate. Thus, shifting the average grain size ofthe diamond powder mixture into a more coarse grain size may lead to aPCD layer with a lower metal content.

The PCD sample tests summarized above in Tables II, III, and IV werecreated from diamond powder mixtures with 2% w cobalt, as noted above,but high diamond content PCD can be formed with more or less cobalt,and/or with varying amounts of other suitable catalyst materials. Forexample the following data shows two examples of PCD with differentamounts of cobalt added to the diamond powder mixture, both pressed atthe same pressure. A high diamond content PCD was difficult to achievein the sample with 20% w cobalt added to the diamond powder mixture, seeTable V below.

TABLE V Nominal Added Hot Cell Grain PCD Cobalt Pressure Size DensityDiamond Metal Diamond Cobalt Tungsten (% w) (GPa) (microns) (g/cm³) (%v) (% v) (% w) (% w) (% w) 2 7.1 5.5 3.992 92.5 7.5 81.4 13.8 4.8 20 7.16.0 4.167 89.4 10.6 75.3 19.8 4.9

Accordingly, as summarized above, PCD with high diamond content can becreated by sintering at higher than normal pressures, and PCD sampleswith high diamond content can be identified as such by assessing thehigh diamond content (by one or more of three methods) and measuring theaverage grain size.

In one embodiment, a polycrystalline diamond (PCD) body contains a firstregion extending at least 300 microns within the diamond body proximatethe cutting edge. The first region has a high diamond content and aplurality of substantially empty interstitial regions. The combinationof high diamond content (with the corresponding microstructure achievedfrom the ultra high pressure conditions used to form the PCD body) andthe substantially empty interstitial regions in a first region extendingdeep into the PCD body unexpectedly provides a cutting element withsuperior performance. The superior performance is especially unexpectedsince the prior art, as discussed above, teaches decreasing thetreatment depth with increasing diamond content in the PCD body.

The first region within the PCD body comprises a plurality ofinterstitial regions that are substantially free of the catalystmaterial. In one or more embodiments, the first region may comprise atleast the critical zone, defined hereinafter. At least a portion of thefirst region extends to a depth within the PCD body of at least 300microns (0.3 mm) from the desired surface or surfaces, for example to adepth of at least 350 microns (0.35 mm), at least 400 microns (0.4 mm),at least 500 microns (0.5 mm), at least 600 microns (0.6 mm), or atleast 800 microns (0.8 mm) in other embodiments. In one or moreembodiments, the interstitial regions may be substantially free of thecatalyst material in at least a portion of the first region to a depthwithin the PCD body of at most 2000 microns (2 mm), suitably at most1500 microns (1.5 mm), more suitably at most 1000 microns (1 mm). In oneor more embodiments, the depth within the PCD body of at least a portionof the first region may be in the range of from 300 microns (0.3 mm) to1500 microns (1.5 mm). Examples of suitable leach depths include 325microns, 375 microns, 425 microns, 450 microns, 475 microns, 500microns, 550 microns, 600 microns, 650 microns, 700 microns, 750microns, 800 microns, 900 microns or 1000 microns. The depth of thefirst region in the PCD body is measured inwardly perpendicular from thesurface of interest of the cutting element to the boundary between thefirst region and an adjacent region. One skilled in the art wouldappreciate that the depth of the first region may be dependent on thediamond table thickness.

In one or more embodiments, the first region may also include areas ofthe PCD body in addition to the critical zone, defined hereinafter, butthese additional areas may not extend to a depth of at least 300microns, for example areas of the first region outside the critical zonemay only extend to a depth of at most 250 microns, at most 200 microns,or at most 175 microns.

The second region within the PCD body containing catalyst material mayhave a thickness that is sufficient to maintain a desired bond strengthbetween the PCD body and the material to which it may be attached (e.g.,the substrate). In one or more embodiments, the second region within thePCD body may extend a distance of at least about 10 microns (0.01 mm),as measured perpendicular from the interface or lower surface of the PCDbody, for example at least 100 microns (0.1 mm), at least 150 microns(0.15 mm), or at least 200 microns (0.2 mm).

In one or more embodiments, the first region 430 may extend along theentire upper surface 422 a of the cutting element 420 as well as thebeveled cutting edge 422 c and a portion of the side surface 422 b, asillustrated in FIG. 4A (viewed in vertical cross-section). In oneembodiment, the first region 430 comprises interstitial regionssubstantially free of the catalyst material. A second region 440 withinthe PCD body 422 between the first region 430 and the lower surfacecomprises interstitial regions containing the catalyst material. PCDbody 422 is bonded to a substrate 424. The depth (or thickness) of asubstantial portion (e.g., at least 75%) of the first region 430 isdepicted in FIG. 4A as being substantially uniform in thickness. Theterm “substantially uniform” as used herein is meant to includevariations in thickness of at most 50%, suitably at most 30%, moresuitably at most 10%. The thickness of the first region 430 along theupper surface 422 a may be substantially the same as the thickness alongthe side surface 422 b and the beveled cutting edge 422 c.Alternatively, the thickness of first region 430 may be greater orsmaller along the side surface 422 b and beveled surface 422 c than thethickness along a major portion of the upper surface 422 a.

In one or more embodiments, the first region 430 may extend along aportion “X1” of upper surface 422 a of the cutting element 420 as wellas the beveled cutting edge 422 c and a portion “Y” of the side surface422 b, as illustrated in FIG. 4B (viewed in vertical cross-section). Thesecond region 440 extends along a portion “X2” of the upper surface 422a. In one or more embodiments, the first region 430 may extend along theupper surface 422 a from the side surface 422 b (along portion X1) atleast 1000 microns, as measured from the side surface 422 b, for exampleat least 1250 microns, at least 1500 microns, at least 2000 microns, atleast 2500, or at least 3000 microns in other embodiments. In one ormore embodiments, the first region 430 may extend along the uppersurface 422 a from the side surface 422 b (along portion X1) less than50% of the diameter “D” of the cutting element 420, as measured from theside surface 422 b, for example at most 30%, at most 25%, such as 20%,15%, or 12.5% of the diameter of the cutting element. In one or moreembodiments, the first region 430 may extend along the side surface 422b (portion Y) at least 300 microns, measured from the lower end ofcutting edge 422 c, for example at least 500 microns, at least 1000microns, at least 1500 microns, at least 2500 microns, at least 3500microns in other embodiments.

The first region of the PCD body having a depth “d” of at least 300microns may extend along at least a “critical zone” when viewed invertical cross-section. The critical zone extends along the length ofthe cutting edge and along the upper surface of the PCD body for atleast 1000 microns, for example at least 12.5% of the diameter of thecutting element, measured from the side surface, and at least 300microns along the side surface, measured along the side surface from thelower end of the cutting edge. The critical zone also extends along atleast a portion of the circumferential distance of the PCD body.Suitably, the critical zone may extend along a major portion of thecircumferential distance of the PCD body, such as along 25% of thecircumference. Suitably, the critical zone may extend along the entirecircumferential distance of the PCD body allowing the cutting element tobe reused on a drill bit without having to undergo an additionaltreatment step.

In one or more embodiments, the diamond crystals (grains or particles)used to form the PCD body may have grain sizes in the range of fromabout 10 nanometers to about 50 micrometers (microns) prior tosintering, for example from 1 micron to 40 microns or from 1 micron to30 microns, in other embodiments. In one or more embodiments, thediamond crystals may have an average grain size of at most 25 microns,at most 20 microns, at most 15 microns or at most 12 microns in otherembodiments. Suitably, the diamond crystals may have an average grainsize in the range of from 1 to 25 micrometers, for example in the rangeof from 2 to 20 microns or from 4 to 10 in other embodiments. Thediamond crystals may have a mono-modal or multi-modal grain sizedistribution. If a catalyst material is mixed with the diamond crystals,the catalyst material may be provided in the form of a separate powderor as a coating on the diamond particles. The catalyst materialfacilitates intercrystalline bonding of the diamond crystals during theHPHT sintering process.

In another embodiment, a PCD body is provided with a bilayerconstruction including a first layer proximate the cutting edge and asecond layer proximate the interface with the substrate. The secondlayer of PCD material proximate the interface (the PCD “bilayer” or the“interlayer”) has more catalyst material and a lower DVF than theremainder of the PCD layer. This bilayer construction can beaccomplished in different ways. In one or more embodiments, the PCD bodymay be formed using two or more diamond mixtures to form differentlayers of the PCD body. In an example embodiment, the first layerforming at least the cutting edge may be formed using at least a firstdiamond mixture comprising diamond crystals having a lower (finer)average grain size than the diamond crystals in at least a seconddiamond mixture used to form the second layer. Alternatively, the firstlayer may be formed using a first diamond mixture comprising diamondcrystals having a greater (coarser) average grain size than the diamondcrystals in a second diamond mixture used to form the second layer.Other options include powder mixtures having the same average grain sizebut differing particle size distributions, and/or powder mixturesincorporating differing amounts of premixed solvent catalyst or otherparticulate additions such as tungsten or tungsten carbide. Inadditional embodiments, three or more layers using different diamondmixtures may be used.

In an example embodiment, the smaller, fine diamond grains in thediamond mixture are removed from the mixture near the interface with thesubstrate. The smaller diamond grains are more difficult to fracture,leading to larger porosity of the diamond body during sintering near thesubstrate, which allows more catalyst material from the substrate toinfiltrate this layer during HPHT sintering. As a result, the diamondbody nearest the substrate has a lower diamond content and a highercoefficient of thermal expansion than the remainder (such as the firstlayer) of the diamond body away from the substrate. This reduces thethermal stresses in this second layer and alleviates crack growth alongthe interface. In general, increasing the average particle size of adiamond mixture can lead to less metal content, due to the fracturing ofthe large diamond crystals and less pressure necessary to achieve agiven diamond content. For example, shifting the diamond crystals fromparticles of 5-15 microns to particles of 10-20 microns may lead tolower metal content in the diamond body for a given pressure. However,the technique described in this example embodiment for a multiple layerdiamond body may not be shifting the average particle size of thediamond mixture as a whole, but rather removing the smaller grains fromthe second layer nearest the substrate interface. This can allow formore catalyst material from the substrate to infiltrate this layer,leading to a higher metal content.

In an example embodiment, a larger amount of catalyst material may beadded to the diamond mixture in the second layer near the substrateinterface (which may include at least a portion of the second region)than in the one or more diamond mixtures used to form the rest of thediamond body (e.g., the first layer which may include at least a portionof the first region). In an example embodiment, the first layer may beformed using a first diamond mixture comprising a catalyst material in aquantity that is lower (lesser amount) than a second diamond mixtureused to form the second layer which may form at least a major (greaterthan 50% v) portion of the second region. After sintering, the diamondbody has a second layer with a lower diamond content (e.g. lower diamondvolume fraction) near the substrate and a first layer with a higherdiamond content away (remote) from the substrate.

In an example embodiment, the first layer of the diamond body may beformed from one or more diamond mixtures having a different particlesize distribution than the one or more diamond mixtures used to form thesecond layer of the diamond body. The second layer may have a higherproportion of coarse-sized diamond particles and fewer fine-sizeddiamond particles, so that there is more space between the coarse-sizeddiamond particles for the catalyst material from the substrate toinfiltrate. This may be accomplished by removing a portion of thefine-sized particles from the diamond mixture used to form the secondlayer. This can lead to an increase in metal content in the secondlayer, near the substrate.

In one or more embodiments, the first region proximate the cutting edgeand at least a portion of the upper surface of a PCD body may containthe catalyst material in a quantity of less than 8% by volume, aftersintering and prior to removal of the catalyst material from theinterstitial regions of the PCD body. Suitably, prior to removal of thecatalyst material from the interstitial regions of the PCD body, thefirst region may contain the catalyst material in a quantity of lessthan 6% v, for example in other embodiments, at most 5.75% v, at most5.5% v, at most 5% v, at most 4.75% v, at most 4.5% v, or at most 4.25%v, same basis.

In one or more embodiments, prior to removal of the catalyst materialfrom the interstitial regions of the PCD body, the first region may havea density of at most 3.88 g/cm3, for example at most 3.87 g/cm3 wherethe first region of the PCD body was prepared using diamond crystalshaving a sintered average grain size of at most 20 microns.

In one or more embodiments, prior to removal of the catalyst materialfrom the interstitial regions of the PCD body, the first region may havea density of at most 3.90 g/cm3 (grams per cubic centimeter), forexample at most 3.89 g/cm3 where the first region of the PCD body wasprepared using diamond crystals having an average grain size of at most15 microns.

In one or more embodiments, prior to removal of the catalyst materialfrom the interstitial regions of the PCD body, the first region may havea density of at most 3.94 g/cm3, for example at most 3.93 g/cm3 wherethe first region of the PCD body was prepared using diamond crystalshaving an average grain size of at most 12 microns.

In one or more embodiments, the cutting element has a first regionhaving diamond volume fraction of greater than 90% by volume (% v), forexample at least 91% v, at least 92% v, at least 92.5% v, at least 93%v, or at least 94% v in other embodiments. In one or more embodiments,the cutting element has a first region having a diamond volume fractionin the range of from greater than 90% v to 99% v, such as 93.5% v, 94.5%v, 95% v, 96% v, 97% v or 98% v. In one embodiment, a first region of aPCD body includes a sintered average grain size less than 25 microns anda diamond volume fraction greater than 92%; and in another embodiment asintered average grain size of at most 15 microns and a diamond volumefraction greater than 92.5%; and in another embodiment a sinteredaverage grain size in the range of from 2.5 to 12 microns and a diamondvolume fraction greater than 92.5%.

In one or more embodiments, the second region may have a diamond content(e.g., diamond volume fraction) that is substantially the same as thefirst region. As used herein, “substantially the same diamond volumefraction” is meant to include variations of at most 2% suitably at most1%.

In one or more embodiments, a major portion (i.e., greater than 50% byvolume) of the second region of the PCD body may have a lower diamondcontent (e.g., lower diamond volume fraction) than the first region. Inone or more embodiments, a major portion of the second region of the PCDbody may have a diamond volume fraction more than 2% lower than thediamond volume fraction of the first region (e.g., proximate theexterior surface of the PCD body), for example at least 3% v or at least4% v lower than the first region. In this embodiment, the diamond volumefraction of the second region may be at least 85%, for example in therange of from 85% to 95%, for example 87.5%, 90%, or 92%. The diamondcontent may change in a gradient or step-wise manner within the PCDbody.

In one or more embodiments, the second region may have a tungstencontent (including tungsten carbide) of at most 15% by weight (% w), forexample at most 10% w or at most 5% w. The amount of tungsten may bedetermined by spectroscopic methods or by chemical analysis. Thetungsten is essentially converted to tungsten carbide during the HPHTsintering operation.

Various cutting elements with a bilayer construction and varyinginterface geometries were tested to determine the yield and to comparethe coefficients of thermal expansion of the substrate, the first PCDlayer (proximate the cutting edge), and the second PCD layer (proximatethe substrate). Approximately 200 cutting elements without a bilayerconstruction and over 1,000 with a bilayer were tested. The overallthickness of the combined PCD layer (first and second layers) was 0.100inches (2.54 mm). The thickness of the second layer was 0.060 inches(1.52 mm). It should be understood that the relative thickness of thefirst layer (the layer having the cutting surface) and the second layer(also referred to as the bilayer) (between the first layer and thesubstrate) may vary. In some embodiments, the second layer has a greaterthickness than the first layer, and in other embodiments the first layerhas a greater thickness than the second layer, or they may be equal.

Characteristics of each component were as follows. The carbide substratecontained 87.0% by weight tungsten carbide and 13.0% cobalt. Thecoefficient of thermal expansion (CTE) of the substrate at threetemperature ranges was measured to be as follows (with “RT” indicatingroom temperature, and temperatures given in ° C.) (note, the carbidesubstrate was tested to a higher temperature than the PCD layers due tothe expansion caused by graphitization of diamond above 800° C.):

Carbide Substrate Temperature Range CTE RT-200 5.86E−06 200-500 6.64E−06500-965 7.32E−06

The diamond powder was sintered with this substrate at higher thannormal HPHT conditions to produce a PCD layer with high diamond content.The second layer contained 94.3% by volume diamond and 5.7% by volumecobalt and tungsten carbide (as determined by the Density methoddescribed above). Percentages by weight were 84.7% diamond, 11.2% cobaltand 4.1% tungsten carbide after sintering. The average diamond grainsize was 12.4 microns. The coefficient of thermal expansion wascalculated as follows (based on a linear extrapolation of data from PCDsamples with lower DVF):

PCD Second Layer Temperature Range CTE RT-200 2.479E−06 200-5003.272E−06 500-800 4.164E−06

The first layer of the PCD contained 94.0% by volume diamond, and 6.0%cobalt and tungsten carbide. Percentages by weight were 85.7% diamond,10.9% cobalt and 3.9% tungsten carbide. The average diamond grain sizewas 13.0 microns. The coefficient of thermal expansion was calculated asfollows (based on a linear extrapolation of data from PCD samples withlower DVF):

PCD First Layer Temperature Range CTE RT-200 2.471E−06 200-500 3.262E−06500-800 4.151E−06

As this data shows, the second layer (bilayer) had a slightly increasedcoefficient of thermal expansion compared to the first layer, therebypartially bridging the gap between the coefficients of the substrate andthe first layer. Although the increase was not large, the PCD cuttingelements with this bilayer construction had a noticeably higher yieldthan PCD without a bilayer. The inventors have found that typical yieldswithout a bilayer are 85-90%. The testing above showed that the yieldwith the bilayer present was above 99%.

Another example of the effect of a bilayer construction is providedbelow. PCD cutting elements with the same material and interface wereformed, and the presence of cracks was noted for cutting elements withand without a bilayer.

TABLE VI Protrusion Hot Interface Ratio Pressure Geometry Yield Cutting0.57 6.2 GPa A5 95% (152/160) elements with bilayer Cutting 0.57 6.2 GPaA5 63% (25/40) elements without bilayer

Interface A5 had the same dome radius as interfaces A1-A4 describedbelow, and a protrusion ratio of 0.57.

In an example embodiment, the PCD body may comprise a bilayerconstruction having first and second layers and a first region withinthe diamond body. As illustrated in FIG. 7 (a vertical cross-sectionalview), a cutting element 720 contains a diamond body 722 bonded to asubstrate 724. The diamond body 722 contains two layers B and C and afirst region A extending into portions of layers B and C. Thus, threedistinct regions may be found within the diamond body: region A formsthe first region and layer C forms the second region, while the portionof layer B positioned in between (interposed) the first and secondregions forms a third region within the diamond body. The second regionmay contain a metal carbide (e.g., tungsten carbide) and have adifferent average diamond particle size and/or particle sizedistribution from the first and third regions. The first region may havethe same average diamond particle size and particle size distribution asthe third region or, alternatively, a major portion of the first regionmay have a different average diamond particle size and/or particle sizedistribution as the third region (i.e., more than two layers are used toform the diamond body). In another example embodiment, catalyst materialmay be added to the diamond mixture used to form the first layer (B),while the diamond mixture used to form the second layer may besubstantially free of added catalyst material. The addition of catalystin the first layer may be useful, as sufficient catalyst material fromthe substrate may not infiltrate to the first layer. In anotherembodiment, catalyst material may be added to the diamond mixture usedto form the second layer (C), while the diamond mixture used to form thefirst layer (B) may be substantially free of added catalyst material ormay have added catalyst in a smaller amount than the second layer. Aftersintering, the second layer has a higher metal content than the otherregions.

In one embodiment, a PDC body such as body 722 includes a bilayerconstruction (layers B and C) as well as a treated region (A) extendinginto portions of the first and/or second layers. The treated region Amay be leached to remove substantially all of a catalyst material fromthe interstitial regions between the diamond crystals. The region A mayextend from a cutting surface to a depth of no more than 100 microns, orin another embodiment a depth in the range of 100 microns to less than300 microns, or in another embodiment a depth of at least 300 microns.The treated region may extend partially into the first layer (B), allthe way through the first layer (B), and/or into the second layer (C).

In an example embodiment, the one or more diamond mixtures used to formthe first and third layers may be subjected to conditions sufficient tographitize at least a portion of the diamond crystals, while the diamondmixture used to form the second layer may not be subjected to conditionssufficient to graphitize at least a portion of the diamond crystals.

One skilled in the art after learning the teachings of the presentdisclosure would appreciate that multiple diamond mixtures may be usedto form the PCD body and may form a gradient (gradual transition) or astep-wise (abrupt) transition within the PCD body. In one or moreembodiments, the cutting element may also comprise a PCD body havingproperties of diamond density, catalyst material concentration, and/ordiamond grain size that change as a function of position within thediamond table. Such variations may occur along a gradient or step-wiseand may provide one or more different properties to the cutting element.

The bilayer embodiments described above provide a PCD layer that has ahigh diamond content at the cutting surface, such that the cuttingsurface has the desired wear resistance and stiffness, while alsoproviding a lower diamond content near the substrate, such that thethermal stresses at the interface surface are reduced. A multi-layerconstruction may be provided, with several separate layers within thePCD layer. The layers increase in diamond content moving away from thesubstrate. The transition between these layers may be gradual, forming agradient, or it may be more abrupt. Instead of a multi-layerconstruction, a single layer may be provided having a density gradient,such that for example the diamond density of the layer graduallyincreases in a direction away from the interface, toward the cuttingface.

Additionally, the bilayer construction may be treated to remove thecatalyst material from a first region of the PCD body, such that thefirst region has a high diamond content and a plurality of substantiallyempty interstitial regions. A second region may include catalystmaterial in the interstitial regions. The first region may extendpartially through the first layer of the bilayer construction, all theway through the first layer, or all the way through the first layer andpartially through the second layer.

As used herein, the term “catalyst material” is understood to refer tomaterials that were used to initially form the diamond layer (i.e., bondthe diamond particles together), and can include materials identified inGroup VIII of the Periodic table (e.g., cobalt). The catalyst materialmay be selected from Group VIII elements of the Periodic table (CASversion in the CRC Handbook of Chemistry and Physics), in particularselected from cobalt, nickel, iron, mixtures thereof, and alloysthereof, preferably cobalt.

As used herein, the term “removed” is used to refer to the reducedpresence of a specific material in the interstitial regions of thediamond layer, for example the reduced presence of the catalyst materialused to initially form the diamond body during the sintering or HPHTprocess, or metal carbide present in the PCD body (a metal carbide, suchas tungsten carbide, may be present through addition to the diamondmixture used to form the PCD body (for example from ball milling thediamond powder) or through infiltration from the substrate used to formthe PCD body). It is understood to mean that a substantial portion ofthe specific material (e.g., catalyst material) no longer resides withinthe interstitial regions of the PCD body, for example the material isremoved such that the voids or pores within the PCD body may besubstantially empty. However, it is to be understood that some smallamounts of the material may still remain in the microstructure of thePCD body within the interstitial regions and/or remain adhered to thesurface of the diamond crystals.

By “substantially free of added catalyst material”, it is understood tomean that no catalyst material, other than catalyst material left as animpurity from manufacturing the diamond crystals, is added to thediamond mixture. That is, the term “substantially free,” as used herein,is understood to mean that a specific material is removed, but thatthere may still be some small amounts of the specific material remainingwithin interstitial regions of the PCD body. In an example embodiment,the PCD body may be treated such that more than 98% by weight (% w ofthe treated region) has had the catalyst material removed from theinterstitial regions within the treated region, in particular at least99% w, more in particular at least 99.5% w may have had the catalystmaterial removed from the interstitial regions within the treatedregion. 1-2% w metal may remain, most of which is trapped in regions ofdiamond regrowth (diamond-to-diamond bonding) and is not necessarilyremovable by chemical leaching.

The term “substantially empty”, as used herein, is understood to meanthat at least 75% of the volume of a void or pore is free from amaterial such as a catalyst material or metal carbide, suitably at least85% v, more suitably at least 90% v is free from such materials. Thequantity of the specific material remaining in interstitial regionsafter the PCD body has been subjected to treatment to remove the samecan and will vary on such factors as the efficiency of the removalprocess, and the size and density of the diamond matrix material. Thespecific material to be removed from the PCD body may be removed by anysuitable process. Treatment methods include chemical treatment such asby acid leaching or aqua regia bath and/or electrochemical treatmentsuch as by an electrolytic process. Such treatment methods are describedin US2008/0230280 A1 and U.S. Pat. No. 4,224,380, which methods areincorporated herein by reference. Treatment by leaching is alsodiscussed in more detail below.

High diamond content PCD bodies created using ultra high pressures havea unique microstructure which in combination with a treatment depth ofat least 300 microns can provide an improvement in one or moreproperties of the cutting element.

In one embodiment, a first region of the PCD body of the cutting elementis treated to remove the catalyst material from a plurality ofinterstitial regions contained therein. Such treatment methods includethose described herein, preferably acid leaching. As discussed above, inone or more embodiments, the first region may comprise the cutting edge,the entire upper surface of the PCD body and at least a portion of theside surface. In one or more other embodiments, the first region maycomprise the cutting edge and only a portion of the upper surface andside surface of the PCD body (e.g., critical zone), and the secondregion or another region containing catalyst material within a pluralityof interstitial regions may extend to a remaining portion of the uppersurface and side surface of the PCD body. The treatment of the firstregion may be accomplished by protecting the outer portions of the PCDbody adjacent the targeted treatment region from contact (liquid orvapor) with the leaching agent. The substrate may also be protected fromsuch contact. Methods of protecting the substrate and/or PCD bodysurfaces include covering, coating or encapsulating the substrate and/orportions of the PCD body with a suitable barrier member or material suchas wax, plastic, or the like.

In one or more embodiments, the first region of the PCD body is renderedthermally stable by removing substantially all of the catalyst materialtherefrom by exposing the desired surfaces to an acid leaching agent, asdescribed herein. Suitably, after the PCD body is made by the highpressure HPHT sintering process, the identified surface or surfaces areplaced into contact with the acid leaching agent for a sufficient periodof time to produce the desired leaching or catalyst material depletiondepth in the first region.

Suitably, leaching agents for treating the first region to be renderedthermally stable include materials selected from inorganic acids,organic acids, mixtures and derivatives thereof. The particular leachingagent used may depend on such factors as the type of catalyst materialused, and the type of other non-diamond metallic materials that may bepresent in the PCD body. In an example embodiment, suitable leachingagents may include hydrofluoric acid (HF), hydrochloric acid (HCl),nitric acid (HNO3) and mixtures thereof. Other methods for leaching thecatalyst material from the PCD body are described herein.

In one or more embodiments, the PCD body has a microstructure such thatit requires at least 3 days under standard conditions, described below,to leach substantially all the catalyst material from the interstitialregions in the PCD body in the first region, to a depth of 300 microns.Suitably, the PCD body may have a microstructure such that it requiresat least 3.5 days under standard conditions, described below, to leachsubstantially all the catalyst material from the interstitial regions inthe PCD body to a depth of 300 microns, or for example at least 4 days,at least 4.5 days, at least 5 days, at least 6 days, at least 7 days, atleast 8 days, at least 9 days, at least 10 days, or at least 14 days inother embodiments. In one embodiment, the standard conditions includecontacting a region of the PCD body with a sufficient volume of an acidmixture at a temperature of 40° C.±2° C. under atmospheric pressure. Theacid mixture is 50% v of a first acid solution and 50% v of a secondacid solution. The first acid solution is 48% w hydrofluoric acid and52% w water. The second acid solution is 68% w nitric acid and 32% wwater. In this embodiment, the first region of the PCD body prior toleaching treatment may have at most 6% w metal carbide (e.g., tungstencarbide), for example at most 5.5% w, at most 5% w, or at most 4.5% w inother embodiments. In this embodiment, the first region of the PCD bodymay have in the range of from 0 to 6% w metal carbide (e.g., tungstencarbide). Subjecting the first region of the PCD body to the standardconditions for a sufficient duration (such as at least 3 days) resultsin the removal of substantially all of the catalyst material from theinterstitial regions in this first region of the PCD body.

In one or more embodiments, accelerating techniques for removing thecatalyst material may also be used, and may be used in conjunction withthe leaching techniques noted herein as well as with other conventionalleaching processes. Such accelerating techniques include elevatedpressures, elevated temperatures and/or ultrasonic energy, and may beuseful to decrease the amount of treatment time associated withachieving the same level of catalyst removal, thereby improvingmanufacturing efficiency.

In one embodiment, the leaching process may be accelerated by conductingthe same leaching process described above under conditions of elevatedpressure that may be greater than about 5 bar and that may range fromabout 10 to 50 bar in other embodiments. Such elevated pressureconditions may be achieved by conducting the leaching process in apressure vessel or the like. It is to be understood that the exactpressure condition can and will vary on such factors as the leachingagent that is used as well as the materials and sinteringcharacteristics of the diamond body.

In addition to elevated pressure, elevated temperatures may also be usedfor the purpose of accelerating the leaching process. Suitabletemperature levels may be in the range of from about 90° C. to 350° C.in one example embodiment, and in the range of from about 175° C. to225° C. in another example embodiment. In one or more embodiments,elevated temperature levels may range up to 300° C. It is to beunderstood that the exact temperature condition can and will vary onsuch factors as the leaching agent that is used as well as the materialsand sintering characteristics of the diamond body. It is to beunderstood that the accelerating technique may include elevated pressurein conjunction with elevated temperature, which would involve the use ofa pressure assembly capable of producing a desired elevated temperature,e.g., by microwave heating or the like. For example, amicrowave-transparent pressure vessel may be used to implement theaccelerated leaching process. Alternatively, the accelerating techniquemay include elevated temperature or elevated pressure, i.e., one or theother and not a combination of the two.

Ultrasonic energy may be used as an accelerating technique that involvesproviding vibratory energy operating at frequencies beyond audiblesound, e.g., at frequencies of about 18,000 cycles per second andgreater. A converter or piezoelectronic transducer may be used to form adesired ultrasonic stack for this purpose, wherein the piezoelectriccrystals are used to convert electrical charges to desired acousticenergy, i.e., ultrasonic energy. Boosters may be used to modify theamplitude of the mechanical vibration, and a sonotrode or horn may beused to apply the vibration energy. The use of ultrasonic energy mayproduce an 80 to 90 percent increase in leaching depth as a function oftime as compared to leaching without using ultrasonic energy, therebyproviding a desired decrease in leaching time and an improvement inmanufacturing efficiency.

In one or more embodiments, the cutting element may also have one ormore intermediate layers as well as planar and non-planar interfaces andsurfaces. Reference may be made to U.S. Pat. Nos. 6,041,875; 6,513,608;6,962,218; 7,604,074; 7,287,610, as examples of non-planar interfacesand such descriptions are incorporated herein by reference. Conventionalcutting elements (shear cutters) incorporate substrates with relativelyaggressive protrusions such as rings and ridges at the interfacesurface, as these protrusions are believed to arrest crack growth in thePCD body by creating alternating areas of tensile and compressivestresses. However, for some PCD bodies with a high diamond content,these stresses should be reduced in order to avoid crack growth, due inpart to higher thermal expansion differences between the substrate andthe sintered PCD material, and also the lower toughness that comes withhigh diamond content.

In one embodiment, the interface between the PCD layer and the substratehas less aggressive protrusions than those provided in the prior art.Conventional shear cutters incorporate substrates with relativelyaggressive protrusions such as rings and ridges, as these protrusionsare believed to arrest crack growth by creating alternating areas oftensile and compressive stresses, as described above. However,aggressive protrusions can also create stress concentrations andincrease the magnitude of the residual stresses in the PCD layer. ForPCD with high diamond content, these stresses need to be reduced inorder to avoid crack growth, due in part to the lower toughness thatcomes with high diamond content. Accordingly, contrary to traditionalthinking, the inventors have discovered that for PCD with high diamondcontent, a smoother interface reduces stress concentrations and crackgrowth.

In an example embodiment, as illustrated in FIG. 9, the interfacesurface 14 of the substrate 16 may have a slight dome, for example thedome may have a constant radius “R” of 1.204 inches (30.58 mm); a height“H” of 0.052 inches (1.321 mm); and a ratio of the height of the dome tothe diameter of the substrate of 0.074. The ratio of the height of thedome to the diameter of the substrate may be at most 0.2, or for exampleat most 0.15 or at most 0.1 in other embodiments.

In one or more embodiments, the interface surface of the substrateincludes one or more protrusions, such as the protrusions 12 and 12′shown in FIGS. 5 and 6. In the embodiments of FIGS. 5 and 6, the height“h” of the protrusion 12, 12′ was measured from the domed surface 14 ofsubstrate 16. The width “w” of the protrusion 12, 12′ was measured athalf of the protrusion's maximum height h. The height-to-width ratio(the “protrusion ratio”) was taken by dividing the height by the width.This definition of protrusion as used herein not only applies togenerally convex shapes extending upward on the substrate surface asshown in FIGS. 5 and 6, but also to generally concave regions or groovesdepressed into the substrate. The smooth domed surface 14 was of heightH and diameter D (referring to FIG. 9). In one or more embodiments, theprotrusion ratio may be less than 0.7, at most 0.5, at most 0.4, or lessthan 0.2, for example in the range of from 0 to 0.5, such as 0.05, 0.1,0.125, 0.15, 0.175, 0.25, 0.3, 0.35 or 0.45. As shown in FIGS. 5 and 6,the protrusions 12,12′ may be rounded and continuously curved (as shownin FIG. 5) or may included flat ends with discrete corners or edges (asshown in FIG. 6).

In one or more embodiments, the interface surface of the substrate mayhave one or more non-aggressive protrusions having a maximum height h,measured from the substrate surface, of at most 0.050 inches (1.27 mm),suitably at most 0.045 inches (1.14 mm), at most 0.040 inches (1.02 mm),at most 0.35 inches (0.89 mm), at most 0.030 inches (0.76 mm), at most0.25 inches (0.64 mm), or at most 0.20 inches (0.51 mm) in otherembodiments. In one or more embodiments, the one or more non-aggressiveprotrusions having a height of at most 0.050 inches (1.27 mm) may bepositioned proximate the side surface of the substrate.

In one or more embodiments, the one or more non-aggressive protrusionshave continuously contoured surfaces. In one or more embodiments, theinterface surface of the substrate has only non-aggressive protrusionsthereon, such as protrusions with a protrusion ratio less than 0.7. Inone embodiment, a PCD cutting element includes an interface with aprotrusion ratio less than 0.7, and a PCD body with a treated firstregion. The first region may extend into the PCD body from a cuttingsurface to a depth of no more than 100 microns, or in another embodimenta depth in the range of 100 microns to less than 300 microns, or inanother embodiment a depth of at least 300 microns.

Substrates with four different geometries having varying degrees ofprotrusion were sintered with a diamond powder mixture to form PCD withhigh diamond content, and the percentage of cutting elements withoutcracks was documented. The percentage of cutting elements that did nothave cracks after the high pressure HPHT sintering process was completedis referred to as the “yield.” As shown in FIG. 9, all of the substrates16 had a slight dome at the interface surface 14. The radius at theinterface surface 14 was a constant 1.204 inches, and the height H ofthe dome was 0.052 inches, as shown in FIG. 9. The ratio of the height Hof the dome to the diameter D of the substrate was approximately 0.074.The thickness of the sintered PCD table was 0.090 inches. The startingdiamond grain size was approximately 14.4 microns, and the hot cellpressure was 7.1 GPa.

Substrates with the four different geometries were combined with thediamond powder mixture and subjected to HPHT sintering at the highpressure conditions in FIG. 11 (in the high diamond content region). Twodifferent sets of process parameters were used to form these highdiamond content cutting elements. A first set of cutting elements wereformed according to a first set of HPHT sintering parameters, includinga brazing process which was performed to add an extension to the cuttingelement. Carbide sections may be joined together to extend the substrateto a longer length. Methods for joining carbide sections together arewell known in the art, and include torch, furnace and induction brazingmethods. Brazing is also commonly known as bonding or LS bonding.Induction methods are commonly used for joining shear cutters carbidesubstrates to longer carbide pieces following the sintering process. Theinduction method is used because it can be employed in conjunction withboth inert gases and heat sinks to protect the PCD from oxidation andthermal damage. However, these methods for joining carbide sectionstogether can cause cracks to form in the PCD layer.

After sintering and induction brazing of the aforementioned cutters wascomplete, the resulting high diamond content PCD cutting elements wereexamined for cracks to determine the yield for each geometry. Theresults of this testing are summarized in Table VII below:

TABLE VII Yield (number without Protrusion cracks/total number tested)-Interface Protrusion Protrusion Ratio first set of process GeometryDescription Height Width (h/w) parameters A1 Relatively 0.035 in 0.046in 0.76  25% (5/20) aggressive, sharp protrusions A2 Relatively 0.045 in0.063 in 0.71  26% (5/19) aggressive, rounded protrusions A3 Less 0.035in 0.064 in 0.55  50% (9/18) aggressive, rounded protrusions A4 No 0 00.00 100% (20/20) protrusions

These results are also shown in the diagram of FIG. 12. The results showthat the protrusion ratio has an inverse linear relationship with yield.The yield improves with decreasing ratio. The geometry that gave thebest yield (A4) was a smooth dome without any protrusions (protrusionratio was zero). This substrate (A4) had a smooth domed surface, withthe radius of the dome being approximately 13 times the thickness of thePCD layer and approximately 23 times the height H of the dome.

Of the substrates that had protrusions (A1, A2 and A3), the substratewith the least aggressive protrusions (A3) had the best yield. Theprotrusion ratio of substrate A3 was lower than that of A1 and A2,meaning that the protrusions were less aggressive in height versuswidth. Substrate A1 had sharp protrusions, while A2 had roundedprotrusions, but the data indicated that this difference did not seem tohave an effect on the yield. The more aggressive protrusions insubstrates A1 and A2 extend up to their full height over a smallerwidth. This more aggressive geometry produced cutting elements with morecracks than the other geometries. The inventors believe that aggressiveprotrusions (such as those having a protrusion ratio over 0.7) causestress concentrations in the high diamond content PCD layer and alongthe interface, which lead to crack growth.

Notably, the diagram of FIG. 12 indicates a linear relationship betweenprotrusion ratio and yield.

A second set of cutting elements with the geometries defined above wereformed according to a second set of HPHT sintering parameters, includeda refinement of the sintering parameters, the PCD bilayer structure, andthe cobalt content. These changes included more consistent processparameters, lower temperature at bonding, and lower cobalt content inthe substrate. The second set of cutting elements had a higher yield;the second set of sintering parameters resulted in an increased yieldfor a given protrusion ratio. The results continue to indicate a lineartrend, with yield increasing with a decreasing protrusion ratio. For thesecond set of cutting elements, the slope of the line was less steep.The first set of cutting elements produce a steeper line, with yielddropping off more rapidly with increasing ratio. Based on the refinedsintering parameters used to form the second set of cutters, the linewas shallower, with yield dropping more slowly with increasing ratio.

These results indicate that the slope of the line in FIG. 12 depends onvariables such as pressure, temperature and brazing. The slope of thecurve fit linking yield and ratio may become steeper with increasingpressure, such as cold cell pressures above 7.0 GPa. The slope may alsovary with refinement of the sintering processes.

Accordingly, in some embodiments, the protrusion ratio is less than 0.2,in order to raise the yield to at least approximately 80%, as shown inthe diagram of FIG. 5. In a preferred embodiment, the protrusion ratiois zero (i.e., no protrusions). In another embodiment, for cuttingelements with high diamond content, a protrusion ratio above 0.5provides acceptable yields. In one embodiment, the protrusion ratio isbetween about 0.5 and 1.0. In another embodiment, a cutting element withhigh diamond content includes a substrate with a protrusion ratio ofzero. The substrate is provided with a smooth dome interface surface andno protrusions.

In one embodiment, the protrusions (such as protrusions 12, 12′ in FIGS.5-6) are positioned inwardly on the interface surface of the substrate,away from the circumferential edge of the substrate, toward the centeraxis of the substrate. As compared to conventional PCD cutting elementsformed at standard pressures, the protrusions for the high pressure PCDcutters are located closer to the center axis of the substrate andfurther from the edge. In one embodiment, the protrusions are locatedwithin a diameter that is approximately 90% of the diameter of thesubstrate, leaving the remaining outer 10% of the diameter proximate theedge free of protrusions. In one embodiment, a substrate with a diameterof 17.8 mm included protrusions that were spaced inwardly from thecircumferential edge of the substrate by 2 mm.

In another embodiment, a substrate with a stepped interface surface isprovided, as shown in FIG. 13. The substrate includes an outer diameterof 0.700 inches. A stepped protrusion is provided in the center of theinterface surface. The step has a diameter and a height. Four differentsubstrates with varying step dimensions were sintered with a diamondpowder mixture at 12.0 ksi to form sintered PCD bodies bonded to thesubstrates. The sintered PCD bodies were then examined for cracks asbefore, and the yield was documented, as shown below in Table VIII:

TABLE VIII Step Step Yield (number Interface Diameter Height withoutcracks/total Geometry (inches) (inches) number tested) B1 0.590 0.030 0% (0/4) B2 0.590 0.040  50% (2/4) B3 0.480 0.030 100% (4/4) B4 0.4800.040  50% (2/4)

The above data shows that the B3 geometry, with a smaller step diametercombined with a shorter step height, gave the best yield. In oneembodiment, the ratio of step diameter to the substrate outer diameteris less than about 0.7.

One additional geometric variable is the thickness of the PCD layer. Athicker PCD layer (or “table”) is likely to have higher residualstresses. Thus, stresses can be reduced by reducing the thickness of thePCD layer. Additionally, for a thicker table, a lower protrusion ratiomay reduce stresses. In one embodiment, the thickness of the PCD tableis reduced as the diamond content is increased.

Optionally, the PCD diamond body may be bonded to a substrate. In one ormore embodiments, the substrate may comprise a metal carbide and a metalbinder which has been sintered (also referred to herein as a sinteredmetal carbide). Suitably, the metal of the metal carbide may be selectedfrom chromium, molybdenum, niobium, tantalum, titanium, tungsten andvanadium and alloys and mixtures thereof. For example, sintered tungstencarbide may be formed by sintering a mixture of stoichiometric tungstencarbide and a metal binder. The substrate may contain metal carbide(e.g., tungsten carbide) in the range of from 75 to 98% by weight, basedon the total weight of the substrate, suitably from 80 to 95% by weight,more suitably from 85 to 90% by weight. The amount of metal binder maybe in the range of from 5 to 25% weight (% w), based on the total weightof the substrate, in particular from 5 to 15% w, for example 6% w, 8% w,9% w, 10% w, 11% w, 12% w, 13% w, or 14% w, on the same basis. In one ormore embodiments, the amount of metal binder in present in the substratemay be in the range of from 6% w to 9% w, or 9% w to 11% w, based on thetotal weight of the substrate. A greater amount of metal binder in thesubstrate may improve fracture toughness of the substrate while a lesseramount of metal binder may improve wear resistance of the substrate, inparticular hardness, abrasion resistance, corrosion resistance, anderosion resistance.

In one or more embodiments, the fully sintered substrate may be preparedby combining tungsten carbide, such as a stoichiometric tungsten carbidepowder, and a metal binder, such as cobalt. The metal binder may beprovided in the form of a separate powder or as a coating on thetungsten carbide. Optionally, a carbonaceous wax and a liquid diluent,such as water or an organic solvent (e.g., an alcohol), may also beincluded in the mixture. The mixture may then be milled, granulated andpressed into a green compact. The green compact may then be de-waxed andsintered to form the substrate. De-waxing may be conducted underconditions sufficient to remove any diluents and wax material used toform the green compact. Sintering may be conducted under conditionssufficient to form the substrate and may use vacuum sintering,hot-isostatic pressing sintering, microwave sintering, spark plasmasintering, etc. During sintering, temperatures may be in the range offrom 1000 to 1600° C., in particular from 1300 to 1550° C., more inparticular from 1350 to 1500° C. As discussed above, the sinteredsubstrate may have a planar or non-planar surface.

The particle sizes of the metal carbide used to form the sintered metalcarbide may also be varied. The particles of metal carbide may be in theform of non-spherical (crushed) particles or spherical particles (i.e.,pellets). The term “spherical,” as used herein and throughout thepresent disclosure, means any particle having a generally sphericalshape and may not be true spheres, but lack the corners, sharp edges andangular projections commonly found in crushed and other non-sphericalparticles. The term, “non-spherical,” as used herein in the presentdisclosure, means any particle having corners, sharp edges and angularprojections commonly found in non-spherical particles. Larger particlesizes of greater than 6 microns, in particular in the range of from 8 to16 microns may be used. Use of larger particle sizes of the metalcarbide may also provide improved fracture toughness. Smaller particlesizes of 6 microns or less, in particular in the range of from 1 micronto 6 microns may also be used. Use of smaller particle sizes of themetal carbide may also provide improved wear resistance of thesubstrate, in particular improved erosion resistance and hardness. Theparticle sizes of the metal carbide may also be multi-modal which mayprovide substrates and cutter elements with various properties. Themetal binder may be selected from Group VIII metals, for example iron,cobalt, nickel, alloys and mixtures thereof. Suitably, the substrate maybe a tungsten carbide sintered with a cobalt binder.

In one or more embodiments, diamond powder containing diamond crystalsor grains (natural or synthetic) may be placed into an assembly with asource of catalyst material. The source of catalyst material may be inthe form of a powder mixed with the diamond powder or in the form of acoating on the diamond crystals. The amount of catalyst materialprovided in combination with the diamond crystals (whether in the formof a powder, tape or other conformable material) may be in an amount ofat most 3% w, suitably at most 2% w. Alternatively, or in addition, thesource of catalyst material may be in the form of a substrate positionedadjacent the diamond mixture in the assembly.

Alternatively, or in addition, the diamond mixture may be provided inthe form of a green-state part comprising diamond crystals andoptionally catalyst material contained by a binding agent, e.g., in theform of diamond tape or other formable/conformable diamond product usedto facilitate the manufacturing process. When such green-state parts areused to form the PCD body, it may be desirable to preheat before theHPHT consolidation and sintering process. The resulting cutting elementcontains a PCD body with a material microstructure made of a diamondmatrix phase of bonded together diamond crystals, with catalyst materialfrom the substrate disposed within interstitial regions that existbetween the bonded diamond crystals. When the source of catalystmaterial may come from two or more sources, such as a powder in thediamond mixture and a metal binder in the substrate, the catalystmaterial from each source may be the same or different. When thecatalyst material infiltrates from the substrate into the PCD body, themetal binder in the substrate has a dominant effect on the metalcomposition in the interstitial regions of the PCD body.

In one or more embodiments, the cutting element may be formed byutilizing a partially densified substrate. As used herein, fullydensified is understood to mean tungsten carbide particles infiltratedwith a metal binder which have zero or no porosity. Partially densifiedsubstrates are described in US 2004/0141865 A1, and such description isincorporated herein by reference. A mixture comprising diamond crystals,as discussed above, may be placed in contact with the surface of thepartially densified substrate and subjected to a high pressure, hightemperature (HPHT) sintering process to form the PCD body bonded to thesubstrate.

In one or more embodiments, the cutting element may be formed byutilizing pre-cemented tungsten carbide granules and forming thesubstrate in-situ during the HPHT process. The pre-cemented tungstencarbide granules and diamond mixture, as discussed above, may be placedin contact within an assembly and subjected to a HPHT sintering process.

In another embodiment, a PCD cutting element has a substrate with areduced coefficient of thermal expansion. This can be accomplished byreducing the cobalt content of the substrate. In one embodiment, thecobalt content of the substrate (prior to sintering) is within the rangeof approximately 6% to 13% by weight. In another embodiment, the cobaltcontent of the substrate is less than about 11% by weight, and inanother embodiment within the range of approximately 9% to 11% byweight. This modification brings the coefficients of thermal expansionof the substrate and the high diamond content PCD layer closer to eachother, which reduces the thermal stresses at the interface. In oneembodiment, a PCD cutting element includes a substrate with a reducedcobalt content, and a PCD body with a treated first region. The firstregion may extend into the PCD body from a cutting surface to a depth ofno more than 100 microns, or in another embodiment a depth in the rangeof 100 microns to less than 300 microns, or in another embodiment adepth of at least 300 microns.

The high diamond content PCD bodies disclosed above may be formed as acutting element for incorporation into a downhole tool such as a drillbit. Referring again to FIG. 1 and FIG. 8, the bit body 12 of the drillbit 10 may include a central longitudinal bore 17 permitting drillingfluid to flow from the drill string into the bit body 12. Bit body 12 isalso provided with downwardly extending flow passages 21 having ports ornozzles 22 disposed at their lowermost ends. The flow passages 21 are influid communication with central bore 17. Together, passages 21 andnozzles 22 serve to distribute drilling fluids around a cutting elementto flush away formation cuttings during drilling and to remove heat fromthe bit 10.

FIG. 8 is an exemplary profile of a fixed cutter rotary bit 10 shown asit would appear with all blades and all cutting elements rotated into asingle rotated profile. Bit 10 contains three primary blades and threesecondary blades.

Still referring to FIG. 8, primary blades and secondary blades areintegrally formed as part of, and extend from, bit body 12. Primaryblades and secondary blades extend radially across bit face 29 andlongitudinally along a portion of the periphery of bit 10. Primaryblades extend radially from substantially proximal central axis 811toward the periphery of bit 10. Thus, as used herein, the term “primaryblade” is used to describe a blade that extends from substantiallyproximal central axis 811. Secondary blades do not extend fromsubstantially proximal central axis 811. Thus, as used herein, the term“secondary blade” is used to describe a blade that does not extend fromsubstantially proximal central axis 811. Primary blades and secondaryblades are separated by drilling fluid flow courses 19 (see FIG. 1).

In one or more embodiments, one or more of the primary blades and/or oneor more of the secondary blades may have one or more back-up cuttingelements positioned thereon. Primary cutter elements are positionedadjacent one another generally in a first row extending radially alongeach primary blade and optionally along each secondary blade. Further,back-up cutting elements may be positioned adjacent one anothergenerally in a second row extending radially along each primary blade,for example in the shoulder region. Suitably, the back-up cuttingelements may form a second row that may extend along each primary bladein the shoulder region, cone region and/or gage region, for example inthe shoulder region. In one or more embodiments, back-up cuttingelements may be provided in more than one row on a blade.

As used herein, the term “back-up cutting elements” is used to describea cutting element that trails any other cutting element on the sameblade (primary or secondary) when bit 10 is rotated in the cuttingdirection. Further, as used herein, the term “primary cutting element”is used to describe a cutting element provided on the leading edge of ablade (primary or secondary). In other words, when bit 10 is rotatedabout central axis 811 in the cutting direction, a primary cuttingelement does not trail any other cutting elements on the same blade.

Suitably, each primary cutting element and optional back-up cuttingelements may have any suitable size and geometry. Primary cuttingelements and back-up cutting elements may have any suitable location andorientation. In an example embodiment, back-up cutting elements may belocated at the same radial position (within standard manufacturingtolerances) as the primary cutting element it trails, or back-up cuttingelements may be offset from the primary cutting element it trails, orcombinations thereof may be used. The primary and back-up cuttingelements may be “on-profile” or “off-profile” or combinations thereof.As used herein, the term “off-profile” may be used to refer to a cuttingelement that has an extension height less than the extension height ofone or more other cutting elements. As used herein, the term“on-profile” may be used to refer to a cutting element that has anextension height that defines the outermost cutting profile of thedrill.

Referring to FIG. 8, blade profiles 39 and bit face 29 may be dividedinto three different regions: cone region 24, shoulder region 25 andgage region 26. Cone region 24 is concave in this example embodiment andcomprises the inner most region of bit 10 (e.g., cone region 24 is thecentral most region of bit 10). Adjacent cone region 24 is shoulder (orthe upturned curve) region 25. Next to shoulder region 25 is the gageregion 26 which is the portion of the bit face 29 which defines theouter radius 23 of the bit 10. Outer radius 23 extends to and thereforedefines the full diameter of bit 10. As used herein, the term “full gagediameter” is used to describe elements or surfaces extending to thefull, nominal gage of the bit diameter.

Still referring to FIG. 8, cone region 24 is defined by a radialdistance along the x-axis measured from central axis 811. It is to beunderstood that the x-axis is perpendicular to the central axis 811 andextends radially outward from central axis 811. Cone region 24 may bedefined by a percentage of the outer radius 23 of bit 10. In one or moreembodiments, cone region 24 extends from central axis 811 to no morethan 50% of outer radius 23. In one or more embodiments, cone region 24extends from central axis 811 to no more than 30% of the outer radius23. Cone region 24 may likewise be defined by the location of one ormore secondary blades. For example, cone region 24 extends from centralaxis 811 to a distance at which a secondary blade begins. In otherwords, the outer boundary of cone region 24 may coincide with thedistance at which one or more secondary blades begin. The actual radiusof cone region 24, measured from central axis 811, may vary from bit tobit depending on a variety of factors including without limitation, bitgeometry, bit type, location of one or more secondary blades, orcombinations thereof. For instance, in some cases bit 10 may have arelatively flat parabolic profile resulting in a cone region 24 that isrelatively large (e.g., 50% of outer radius 23). However, in othercases, bit 10 may have a relatively long parabolic profile resulting ina relatively smaller cone region 24 (e.g., 30% of outer radius 23).Adjacent the cone region 24 is the shoulder (or the upturned curve)region 25. In this embodiment, shoulder region 25 is generally convex.The transition between cone region 24 and shoulder region 25 occurs atthe axially outermost portion of composite blade profile 39 (lowermostpoint on bit 10 in FIG. 8), which is typically referred to as the noseor nose region 27. Next to the shoulder region 25 is the gage region 26which extends substantially parallel to central axis 811 at the outerradial periphery of composite blade profile 39.

In one or more embodiments, one or more cutting elements of the presentdisclosure (first cutting elements) may be positioned on the bit aloneor in combination with one or more second cutting elements which aredifferent (i.e., not in accordance with the cutting elements of thepresent disclosure). The cutting elements of the present disclosure maybe positioned in one or more areas of the drill bit which will benefitthe most from the improved properties/performance of such cuttingelements. Such areas of the drill bit may include the nose region,shoulder region and/or gage region of the drill bit. In one or moreembodiments, the cutting elements of the present disclosure may bepositioned on the drill bit as primary cutting elements in the nose,shoulder and/or gage regions while the second cutting elements may bepositioned on the drill bit as back-up cutting elements in these regionsas well as primary cutting elements in the cone region. In one or moreembodiments, the cutting elements of the present disclosure may bepositioned on the drill bit as primary cutting elements and as back-upcutting elements in the nose, shoulder and/or gage regions of the drillbit while the second cutting elements may be positioned as primarycutting elements in the cone region.

Such cutting elements as described herein may be used in any number ofapplications for example downhole tools such as reamers, bi-center bits,hybrid bits, impregnated bits, roller cone bits, milling bits, as wellas other downhole cutting tools.

In one or more embodiments, prior to removal of the catalyst materialfrom the interstitial regions of the PCD body, the PCD body may have adry vertical turret lathe (VTL) cutting distance of at least 5,500 feet(1,675 meters), for example at least 7,500 feet (2,285 meters), at least10,000 feet (3,050 meters), at least 11,000 feet (3,350 meters), atleast 12,000 feet (3,655 meters), at least 13,000 feet (3,960 meters),at least 14,000 feet (4,265 meters), or at least 15,000 feet (4,570meters) in other embodiments.

The VTL cutting distance is measured by the following VTL test method. ABarre granite rock sample is used to measure the VTL cutting distance.The rock sample having an outer diameter of 36 inches (914 mm) and aninner diameter of 12 inches (305 mm) is mounted on a vertical turretlathe to present a rotating surface of rock to the cutting element. A 16mm diameter cutting element is mounted with a negative back rake suchthat the central axis of the cutting element forms a 20° angle with aline normal to the surface of the rock sample. A 45° chamfer is employedon the cutting edge of the PCD body of the cutting element. The chamferhas a width of 0.012 inches (0.3 mm). The vertical turret lathe isadjusted to advance the cutting element radially toward the center ofthe rock sample as the rock sample is rotated below the cutting elementto produce a spiral kerf in the granite table extending from the outeredge of the rock sample to the center. The vertical turret lathe isoperated under conditions sufficient to provide a cutting feed rate of0.02 inches/revolution (0.5 mm/rev). The surface speed of the cuttingelement over the rock sample is 350 feet/minute (107 meters/min). Thedepth of cut (Z direction) is 0.08 inches (2 mm). The test is conductedunder dry conditions, i.e., no coolant is used during the test. Themeasured VTL cutting distance is the distance of rock cut up to thepoint in time of cutter failure, i.e., no more rock is cut with thecutting element being tested. Typically, cutter failure is indicated bylight being emitted by the cutting element and/or graphitization of thecutting element leaving a black mark on the rock sample. The VTL test isconducted on the PCD sample prior to leaching (if any). The VTL cuttingdistances given above identify the tested PCD sample as a sample withhigh diamond content.

The various embodiments described above may be used independently or maybe used together; for example, a PCD body may have a bilayerconstruction and/or the coefficient of the substrate may be reducedand/or the substrate geometry may be modified to be less aggressiveand/or leached to a depth of at least 300 microns. PCD cutting elementswith some or all of the features described above are most useful forsintered diamond grain sizes approximately 20 micron or less, as diamondgrains greater than 20 micron typically do not have the necessary wearresistance for shear cutter applications. In one embodiment, the diamondgrain size is approximately 15 micron or less. Embodiments of thepresent disclosure may be practiced with larger grain sizes as well.

High diamond content cutting elements of the present disclosure candrill through an earthen formation for longer periods of time and/or athigher speeds, higher weight on bit (WOB) and/or higher rates ofpenetration (ROP) than cutting elements known heretofore. The cuttingelements of the present disclosure can drill through highly abrasiveearthen formations (e.g., sandstones and geothermal applications) whichwere not amenable to drilling with fixed cutter drill bits heretofore.The enhanced treatment of the PCD microstructure resulting from the useof ultra high pressures when forming the PCD body can result in improvedstrength (e.g., transverse rupture strength), impact resistance,toughness, thermal stability, wear resistance, and/or reduced crackingas compared to cutting elements prepared using similar compositions butlower processing pressures and/or shallower treatment depths.

In particular, leached PCD cutting elements with high diamond contentmay show an improvement in transverse rupture strength compared toleached cutting elements formed at standard pressures. In conventionalcutting elements, leaching the PCD body to remove the catalyst metalfrom the interstitial regions can reduce the strength of the PCD body.Thus leached conventional PCD cutters have reduced strength compared tounleached conventional PCD cutters. With high diamond content cuttersaccording to the present disclosure, the loss in strength thataccompanies the leaching process is less significant; that is, thedifference in strength between leached and unleached cutters is lowerwith the high pressure, high diamond content cutters. In one embodiment,the inventors have observed this improvement in strength for highpressure PCD cutters formed with fine diamond grains (sintered averagegrain size below 10 microns).

While the present disclosure has been described with respect to alimited number of embodiments, those skilled in the art, having benefitof this disclosure, will appreciate that other embodiments can bedevised which do not depart from the scope of the invention as disclosedherein. Accordingly, the scope of the invention should be limited onlyby the attached claims.

What is claimed is:
 1. A method of forming a polycrystalline diamondcutting element with high diamond content, comprising: providing acatalyst material and a plurality of diamond particles; subjecting thecatalyst material and the diamond particles to a high temperature andhigh pressure process, comprising applying a cold cell pressure withinthe range of approximately 5.4 GPa to 6.3 GPa and a temperature withinthe range of approximately 1400 to 1500° C., thereby forming apolycrystalline diamond body comprising a plurality of bonded-togetherdiamond crystals and interstitial regions between the diamond crystals,and comprising a cutting edge; and removing the catalyst material from afirst region of the diamond body proximate the cutting edge to render aplurality of the interstitial regions in the first region substantiallyempty, the first region extending to a depth of at least 300 micronsfrom the cutting edge.
 2. A method of forming a polycrystalline diamondcutting element with high diamond content, comprising: providing a firstdiamond mixture; providing a second diamond mixture; and subjecting thefirst and second diamond mixtures to a high temperature and highpressure process in the presence of a catalyst material, such hightemperature and high pressure process comprising applying a cold cellpressure within the range of approximately 5.4 to 6.3 GPa and atemperature within the range of approximately 1400 to 1500° C., therebyforming a polycrystalline diamond body comprising a first layer formedfrom the first diamond mixture and a second layer formed from the seconddiamond mixture, each layer comprising a plurality of bonded-togetherdiamond crystals and interstitial regions between the diamond crystals,wherein the first layer forms at least a portion of the cutting edge ofthe diamond body and has a first diamond volume fraction, wherein thesecond layer forms at least a portion of an interface surface of thediamond body and has a second diamond volume fraction that is at leastapproximately 2% less than the first diamond volume fraction, whereinthe first layer comprises a sintered average grain size less than 25microns, and wherein the first layer has at least one of the followingproperties: an apparent porosity less than (0.1051)·(the average grainsize ̂-0.3737), or a leached weight loss less than (0.251)·(the averagegrain size ̂-0.2691), or the first diamond volume fraction is greaterthan (0.9077)·(the average grain size ̂ 0.0221), with the average grainsize provided in microns.
 3. A method of forming a polycrystallinediamond cutting element with high diamond content, comprising: providinga plurality of diamond particles and a substrate material having acobalt content of less than approximately 11% by weight; and subjectingthe diamond particles and the substrate material to a high temperatureand high pressure process, comprising applying a cold cell pressurewithin the range of approximately 5.4 to 6.3 GPa and a temperaturewithin the range of approximately 1400 to 1500° C., thereby forming apolycrystalline diamond body comprising a plurality of bonded-togetherdiamond crystals and interstitial regions between the diamond crystals,wherein at least a portion of the polycrystalline diamond body comprisesa sintered average grain size less than 25 microns, and wherein theportion of polycrystalline diamond body has at least one of thefollowing properties: an apparent porosity less than (0.1051)·(theaverage grain size ̂-0.3737), or a leached weight loss less than(0.251)·(the average grain size ̂-0.2691), or the first diamond volumefraction is greater than (0.9077)·(the average grain size ̂ 0.0221),with the average grain size provided in microns.